A833OD will be the easiest. It fits without welding.

It is not the best, although the lighter A-body weight removes some of the problems of the huge ratio drops.

Probably the R154 Supra Turbo 5-speed is next, I believe it doesn't require modifying the torsion bar crossover, could be wrong. But the shifter is in a different place, IIRC.

Problem to me is that on a linear scale, "easy" is at one end of the scale and "best" is as far away as it can be. So while a modern 5 or 6 speed built to handle mountains of torque is best, it is also the most difficult to actually install in the car. And the A833OD is easiest but its large gear splits make it also the worst.

Get the picture?

R.