Use bellhousing from 760/780 V6 83-90. There's one in the JY I'll pull for you if you want. I think you can keep your converter and driveplate (same IIRC).
Converter housing is removable, but different between 3 and 4-speed. Install 240TIC shift kit and high stall converter if you wish as well as 240T police car trans cooler (same as a 740, just with T-static bypass in some years and braided hoses running through the front sheetmetal). Optional with towing package.
Sort out the x-member and driveline, shift linkage is the same. THe Bw/AW55 is 3/4 of an AW7x, just doesn't have the overdrive behind the pump in the converter housing, and has a different valvebody arrangement (obviously).
B280 running on the K-lambda is nice. Would make a nice runner with some B280E heads and machined distributor with the eagle liners and pistons for 3L, as well as some ported eagle exhaust manifolds. They really really revised those engines when they went to even fire and fixed every little stupid nitpick thing on them, except for the gaskets on the cylinder liners, which are always kind of a PITA.