Which OD Trans

You actually don't have many choices UNLESS you don't mind chopping up the floor/ crossmember I'm referring to the upper part where the T bars mount. There's threads on about any of these

There's a thread on here about adapting the GM 200R4 or 2004R

You can put an A500/42R_ but you still need some crossmember mods

The larger 727 based A518/ R46 series needs floor mods

Then there's aftermarket like Gearvendors, I don't know who else