Can someone explain and suggest a transmission

[Hank70SS]

With it's cast iron center support for the concentric shafts, the TH400 is probably still the toughest trans in that group, but no overdrive. For everyday use you won't see any difference over the 350.

The 200R4 and 700R4 are close, the 200 was rated for a bit more torque than the 700. The 200 is also the same length as the TH350 so you don't have to have the drive shaft chopped if you go that route. The 200 and 700 both have an overdrive gear and locking torque converter. The locking torque converter will require the wiring and electronic control or you can run without it, you still get a fourth overdrive gear. The 200 came with different bell housings so it could be used on multiple GM engines. If you go 200R4 you need to make sure it has a Chevy bell housing.

Can't speak to the durability of the 200 or 700 for racing.

I'm sure someone with more experience will add more. Brian Henderson but a 700R4 in his 70 last year. Don't believe he races it though.