Bellhousings...
The aluminium bellhousings generally have bolt patterns for both 3-speed and 4-speed transmissions. These are relatively easy to find, I would suggest, in pickups with the overdrive 4-speed.
That transmission might be a good choice for your friend, too. Low first gear, overdrive for cruising, it's just like adding an overdrive top gear to what he has already.
I'll have to check the transmission mount location, however.
Ray