Just throwing out some suggestions too - the 700r4 is longer than the 200r so you might need to shorten the driveshaft. You can build (or buy) either to handle the power from a stroked 350 no problem. The swap is much easier going to an automatic.
The difference would be the closer 1st and second gears in the 200 - which shaves a few hundredths of a second off 1/4 mile ET; and the smaller one has a .67:1 final ratio, so it'll have lower RPMs on the highway - like chevyII said. The 700r4 is bought because it's durable, strong, and for the low 1st gear. Take your pick
