Toyota R154 5 speed?

It’s a very good transmission, and there are lots of aftermarket upgrades for them. They can be mounted to a SBM using a Dakota bell housing from the right year range.

The only issue is that you’re on your own for crossmember fabrication and there’s the hydraulic throw out conversion. Tunnel mods are also required, probably less substantial than what’s needed for a T56 but they are significant.

And they can be expensive, the Supra crowd pays a bunch for them.

@Buschi340 put one behind a 340 and then a 6.1 in his Dart