Best trans for a manuel swap?

nv3500 would stink with 3.91 or 3.73 gears. Might work okay with a 3.23 or numerically lower gears. first gear is pretty low so even with 3.23 gears your coming out of the hole like 3.91 gears. but then the overall gear spread is wider. There is a wide ratio and a close ratio, you would want the close ratio. I think the nv3500 is good to around 300hp

most T56 trans have pretty good gear ratios. From what I have read some are good to 330 hp and some are good to 550 depending on what they came from. t56 is without a doubt the superior transmission but likely more money as well.