So I recently got a donor slant 6/904 out of a parts car. I left the old transmission in the project vehicle (a 1975 Duster) and while attempting to install the engine, I had a problem. The engine would go all the way onto the torque converter, and then stop in the last quarter inch - a few millimeters before the guide pegs would slot in. I have no idea what I'm doing wrong so any help is appreciated.

What year was the engine?

1967 and older engines won't mate to 68 and later transmissions.

67 and older transmissions can mate to 68 and newer engines with an adapter ring and crankshaft flange.

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Also, sometimes all of the splines and pump drive pieces do not get engaged when you slide the converter into the trans. Try removing all load from the converter (back trans away from engine, if anything is touching the conv) then rotate the converter around while pushing it lightly toward the trans. When it slips all the way in, the engine will not touch the converter when you get the guide pins and engine/trans flanges mated. Do not force anything or you can break something in the converter or trans input/pump systems.

Another possibility is that you have substantial crud/dirt/damage/rust on the torque converter snout (1.815" large "pin") or on the receiver hole inside the crankshaft.

Lou

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Home of Slant6-powered fun machines

Will try that. It's a 1975 trans and a 1976 cast-crank slant. the input shafts on both of the transmissions looked identical. I don't think there's any damage to the torque converter as i pulled the transmission off of it after I removed it from the car.

So the torque converter mounting blocks (four bolts to flex plate) aren't supposed to stick out from the bell-housing at all?

That's correct. If the torque converter is fully seated into the transmission, the engine block will sit flush against the bell housing before the flex plate touches the mounting blocks.

After you have the bell housing bolted up, there should still be clearance to spin the converter around while you match up the mounting holes (they are not perfectly spaced and only match up 1 way, I think). Installing the flex plate to convertor bolts will pull the convertor forward some small fraction of an inch.

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

alright, back to the garage for me then. I've been swearing at this car all day while doing it wrong.

Edit: changed "gently push" to "several healthy smacks with a rubber mallet" and it looks like it's good to go now. Thanks for the help!