I should have mentioned it in my previous post, but better late than never. The best money you can spend at this point is to purchase a factory shop manual, which should answer most of your questions. There on E bag in both CD and paper form.

Dogdays did a nice writeup on his 64 truck but unfortunately his is a completely different setup than the Plymouth (which among other things does in fact have a transmission cross member). I could do a writeup on what needs to be done, but it would be from memory and rather lengthy and you will find all the info in the service manual.