try 2.93:1 diff it works the best, I did it before with 3.25:1 its good but high rpm on the freeway, for example 100 mph @5800rpm. but better acceleration, I beat mustangs, camaros and vetts but mine is with M3 engine and some mods. I just fired up my m50 conversion this weekend after 160 hours of straight labor. The beasty started right up after priming the pump and is running well for the most part. I'll have to change out the diff as my current top speed is around 80 mph with the 410...but it shure does get there quick :) I will post some pictures soon!