Transmision options.

Professor Fate said
Easiest? Least mods? Smallblock 727 or a 904. Get the appropriate flexplate, bolt it together and go. Well, maybe not THAT easy, but pretty much. No trans controller needed, no crossmember or floorpan mods needed.
I'm assuming you're talking about a later A body, not a '66 or earlier.

Correct. 74 Sport to be exact. And I have a couple 904 cores, but thought the 518 I have would be better for potential longer distances, highways. And since neither motor or transmission are in the car, a little mod wouldn’t be bad. But it’s rapidly approaching information overload when trying to marry up Hemi and 518 overdrive.