A904 transmission for 318

And the PT KD mechanism can be retrofit down to 67 IIRC, AND
the slanty trans may have the required parts.

However, I gotta tell ya that the stock A904 from a 71 Demon is likely the all-time best shifting transmissions I was ever lucky enough to drive. Almost Immediately, I pulled that trans out and built 3 or 4 clones, kept the 71, and installed one of the clones. That was 1976.
I still have at least one clone and the original Demon trans.