Thank you for that.

The recipient car is 1230531001961 from 1978. The donor with the 5-speed is from 83 or 84.

How the relatively wide crossmember on the long transmission could fit in the narrowing tranny tunnel is hard to explain -- unless it was bolted into the floor pan, which seems unlikely.

Ill get the number of the donor. (It's driving me crazy, but the auto shop doing the swap has mislaid the donor driveshaft, so I cant answer the driveshaft part of the puzzle yet.)

Finally,, there are four fixing holes for the tranny crossmember. The 5-speed would appear to need a crossmember using the narrowest set. Does that correspond with your piece?