Stop in for a cup of coffee

Transmission builder will likely opt for swapping your tail end onto rebuilt one. If i was in the same situation i would modify transmission mount and shorten driveshaft.
But, i would have pulled transmission from car and have it rebuilt. This way there are no fitment issues.

Yeah... Lesson learned for sure. The far better path would be to just get this one rebuilt and then it slides right back in. I'll see if he has a market to sell the one that I bought and is willing to do the work on this older one.

I had planned to have the car on the road as long as possible while getting ready but the old transmission finally went T-U and trashed my plan.