I can share a similar vibration experience if worth anything for consideration:
I had a 77 Dodge van with a 360 ci and bad tranny and I had a good tranny off a 318 ci engine in storage. I swapped the trannies and the one from the 318 buckled right up to the 360!
The problem was, the harmonic balancer in the 318 (that I left in that tranny) wasn't balanced for the 360... so I had vibration until I replaced the balancer.
Good luck!
Jerry
