I dont think any 6 had the same bell housing bolt pattern as the small block. However, you might be able to just swap out the 6cly bellhousing on the tranny to one that will fit a 302. I'm not sure if a 6cyl C4 is any different internaly.
The C4 had a removeable bellhousing, so you'd need to find the engine plate, flexplate, torque converter, & bellhousing for a V8 C4 - it should bolt up.
I took a C4 w/ bellhousing and torque converter from a late 70's Granada with a six, and bolted it up to a '67 289. I left the origional 289 flexplate on the motor.
Is there a source for info to learn what goes with what? Ideally, I'd like to get a donor car to strip, but that may not work out, so I'll have to mix and match.
heres a good place, just ask. See how many replys you got. Fordbarn.com is obviously about fords, but it usualy takes longer as its not as big, and there are a lot of the same people here and there
What would cause it to be out of balance? I am doing kind of the opposite, I have a 240 six in my truck and have a C4 with a 302 bellhousing and flywheel. i always thought they were different until just now.