Within the context of my Slant 6 Engine swap, I would like to upgrade to a dual circuit master cylinder.

How does one compare different master cylinders to determine which will be the most effective?

If the bore size is the same, and the stroke length is about the same, can one Master cylinder be swapped for the next?

The reason I ask, is that the Master I was planning on using will no longer fit. It is too tall and gets in the way of my clutch release system. (the M.C. is under the floorboards, not on the firewall) I have found a ford master cylinder that may work, if all there is to the MC selection is stroke and bore.

Interested to hear your thoughts and experience.

The MC bore diameter will determine how stiff the pedal is, and how easy it is to modulate the brakes. A larger bore diameter will provide less "hydraulic advantage," because you're attempting to move more fluid through the system (into your calipers/wheel cylinders) per unit of pedal travel. This results in a stiffer pedal, where you need more force on the pedal to actuate the brakes. Certain drivers with gorilla legs (like me) prefer this. A smaller MC bore diameter is like using a longer lever arm (or more pulleys in a block and tackle assembly). It requires less force, but more movement at the point of force application to achieve the same result. This results in a softer brake pedal, which can be easier for you to modulate and avoid lockup. The risk there is that the pedal goes all the way to the floor before you get all the braking pressure you need.

Bore diameter at the calipers/wheel cylinders is the opposite. A larger diameter here means more linear motion is necessary to achieve the same fluid movement on the pads/shoes (softer pedal). Generally speaking, if you're using parts from the same manufacturer it's good to stick with the same year range for both front calipers and master cylinder. You can then play with the diameter of your rear calipers/wheel cylinders to balance the brakes for your vehicle. You can also add an adjustable proportioning valve to the rear line if the rears are locking up too early.

As far as I know, stroke length is only important insofar as you have enough travel to get all the brake pressure you need before it bottoms out.

Are you building a custom roadster, or am I thinking of someone else? Front disc/rear drum? If the big four-bolt master cylinder seen here won't fit your application, you can also use this later two-bolt unit. I believe these are both 1-1/32" bore diameter.

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Somehow I ended up owning three 1964 slant six A-bodies. I race one of them.
Escape Velocity Racing

The first question is what type of brakes are you running? Drums? Discs?