Is there a picture in the Factory Service Manual or other showing the way to adjust brake pedal height on a 1963 Valiant?

I lifted the pedal higher than normal when I popped the rod from the back of the old MC (after placing some spacers between the MC and firewall).
Now with the 72 MC installed, the pedal is too high.
When I'm sitting in the driver seat and moving from the gas pedal to the brake, it feels wrong.

The brake light switch is working and I checked whether its braket could be adjusted so the brake arm contacts it sooner, but that doesn't make much difference.
The brake light switch contacts the end of the actuator rod where it connects to the pedal arm and the switch's bracket contacts the arm after the switch is depessed - it seems right, but the pedal is too high.

Something moved when I pulled up on the pedal, but I can't figure it out.
The distance from the back of the pedal to the carpet is 7 3/4", and I think it should be around 6" for it to be close to the gas pedal's height.

Right now the bracket that holds the brake switch is what is preventing the pedal from going higher.

There was a long "pulling" spring added a couple years ago to pull the brake pedal high enough to reliably turn off the brake lights when the brakes are released,
and that's another reason the pedal is so high (I think that spring is unnecessary now).

You've got a couple of issues going on here that need to be fixed. The brake lamp switch is not meant to be used as a brake pedal stop, tempting though it may be. Doing so stands you a good chance of ruining the brake lamp switch. There should also never be a "pull up spring" installed as you describe. If the pedal is not being returned fully to the rest/brake-off position, it's because something is wrong.

Pedal too high: Are you sure the master cylinder you installed has an undamaged rubber bushing installed in the counterbore in the rear piston, and that the pushrod's forward end is all the way seated in the new master cylinder you're using? Sometimes it takes a real effort to get the pushrod to seat. Try standing hard on the brake pedal with both feet and as much weight as you can apply. You may find the brake pedal "pops" down to a lower position.

If not, then either a shorter pushrod or spacing the master cylinder out off the firewall slightly is your fix. Shorter pushrods are hard to find (you could use one of the adjustable-length pushrods available—I eventually abandoned mine because it could not be adjusted short enough to drop the pedal to where I wanted it). If you choose to space the master cylinder off the firewall, do so in a careful and quality-conscious fashion: Get a 1/4" plate shaped like the mounting flange of the master cylinder, place it on the firewall studs, then place the master on the studs and tighten down securely.

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Too many people who were born on third base actually believe they've hit a triple.

The switch bracket is now working as the brake pedal stop, not the switch.
The switch contacts the end of the rod and the arm stops against the switch bracket about 3/8" later, before the switch bottoms out.

What part is supposed to be the brake pedal stop?

The pulling spring is no longer necessary.

Right now if I somehow adjust the pedal about 5/8" lower (like spacing the master), the brake switch will not work.
The rod will no longer contact the switch.

I went from a 1963 single MC to a 1972 dual MC and used the old rod.

The way it was put together for the old master cylinder was wrong, but now I need diagrams or photos to see how it is supposed to be assembled.

Is there a missing bracket on the pedal arm that is supposed contact the switch? If not, then the pedal height is correct, because if it was lower the brake lights will stay on all the time.

I can't adjust the brake light switch so it's closer to the floor.
If there is no missing part and the switch didn't move, then the pedal's pivot point must have changed (which is impossible) or the arm got bent (which is impossible)...

Something's bent up or otherwise rigged — maybe you don't have the right brake lamp switch. The brake lamp switch is meant to be actuated by the brake pedal arm itself, not the brake pushrod.
I'd help if I were closer to my car! I'm sure someone can get under the dash of his A-body and shoot some pictures.
No, the arm itself contacts the switch when everything's bolted together correctly. The brake lamp switch and bracket is supposed to look like this:




When all the right parts are installed the right way, the switch bracket is adjustable relative to the dash brace to get correct brake lamp operation regardless of pedal height. If that's not enough adjustability, there's a different, threaded-shank switch you can install in the correct stock switch bracket, that will give you more room to lower the pedal and still have correct brake lamp operation.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

OK. That is the switch I have, but apparently its bracket is bent so it is not lining up with the arm.

What part limits the arm's height?

If I line up the switch with the arm, then the switch will be the only thing stopping the upward travel of the arm. That will cause the switch to fail early.

There is no pedal stop on these cars, per se. The original master cylinders had a plate secured to the rear of the mounting flange, which surrounded the pushrod and held a pushback spring and rubber boot. The rearward travel of the master cylinder piston was stopped by contact with this plate. Some later master cylinders, maybe including your '72 unit, have a snap ring at the rear of the master cylinder bore to stop the piston's rearward travel. Either system acts effectively as a travel stop.
Yep. Sounds like you need to pick up a replacement switch w/bracket (those pictures were from current Ebay auctions) and either find a shorter pushrod or space the master off the firewall to get everything working the way you want.

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Too many people who were born on third base actually believe they've hit a triple.

OK. I'm pretty much resolved to get another master cylinder and start over.
I "bench-bled" the MC on the car (about 30 cycles - I did not have a 2nd person to watch the bubbles). Then I bled the whole system twice, starting with the right rear. The pedal is too low when brakes are applied.
So with the pedal sitting at about 7 3/4", there is probably 3" of travel before there is braking action. That doesn't seem right...

I can't tell if the rod is too short or too long. The directions say to use the old rod, but should I try to get one for a 72?
Or are all the rods for the cast iron single and dual types the same length?

The added spring: I think the spring that goes over the boot (3-4" coil compression-type) must be weak if the extra spring is needed for the brake lamp switch action.
Where can I get that spring, or do I have to use a hardware store spring??

H'mmm...something's definitely the matter if you've got 3" of free play before there's any braking action. Could be air in the lines or in the master, could be lack of a rear-stop for the master cylinder piston, could be a bad master cylinder (what is this, a rebuilt of some kind?), could be an improperly-installed pushrod.

I don't know where to find those aux springs w/boot and retainer new. Can't think of a hardware store spring that would work, either.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

I removed the switch assy and the bracket was bent. I shaped it like the one in the picture and now the switch contacts the arm OK. That lowered the pedal about 3/4 of an inch.
The arm presses the switch and stops by itself.
Yeah, it's a rebuilt MC.

I think one reason the pedal was so high was the extra rubber in the master cylinder socket.
I bench-bled, mounted it to the firewall, removed to bench-bleed again, and mounted it again to the firewall.

When I decided to get a different master cylinder, I pulled it from the firewall again.

I found two rubber rings stacked inside the socket that the rod fits in.
Apparently that grommet/bushing shears when you pull the rod out and half of it stays inside the MC.

It took less effort to "pop" the MC off the last time, so I'm thinking the rod was not seated fully into the socket because of the extra material holding it up.

1/8 inch at the rod translates to about 1/2 inch at the pedal