727 Tail Swap

Trying to figure out if it's possible to swap the tail on between two 727 transmissions (sorry for the similar thread but it got jumbled up with my engine questions!)

Goal: Put a 400 BB into a 1969 A108.
Required: Transmission that mates to the 400 but has the tail with the top hanging mount and shorter length to fit the drive shaft.

Part that I have:
400 BB and matching 727 transmission from a 1976 B-series van
727 transmission from 1969 A108 van (and stock 318 LA engine)

I read that around 1976 the tails could not be interchanged with earlier 727 transmissions. However, this site doesn't mention any incompatibilities between the '69 and '76.

Anyone done this swap? How much work is it and can/should I rebuild the transmission and install a transgo shift kit at the same time?

PXL_20201125_203052315.jpg

PXL_20201125_203030482.jpg