Hi all. Being new to this i posted a detailed description of my problem on another part of the site. Anyway, a helpful member redirected me here. I've just bought a '69 Chevelle that was fitted with a healthy 402 BB about 5 weeks ago. It has a 3200 stall, a 4.10 open diff and a stock TH350 trans. Anyway, the inevitable happened on the dyno today. The trans has destroyed itself (i was having problems with it anyway) and it has split the bell housing right through, and now slipping, so it's toasted. I got on the phone and ordered a B&M street/strip TH350 trans locally, but now i'm not sure. Am i better to get the B&M TH400 (for extra money), even though i need a new yolk etc?. It's a very expensive exercise here in New Zealand. The 'built' TH350 will owe me around $3500 fitted with the TH400 costing $600 more plus drive shaft mods. The car made around 420HP and approx 450 ft/lbs of torque. What do you think?. It's raced once a year and the rest just street use.

You''ll be fine with TH350 behind your build 402...my old 442 clone has been running high 11's for 10 years with a TH350 and a built aluminum headed 455

The TH350 will be fine as long as it is how you described being built. A stock one would not last a long time.
The benefits of the 350 not only being cheaper, it weighs less, has a lower 1st gear ratio, and it is not as parasitic of power as a TH400.