If you're talking about a TH400 transmission, yes... the TH350 torque converter is one inch smaller in diameter than the TH400 torque converter (12" vs 13"), and you'll have to make sure the holes on the flexplate line up (or drill them for both patterns). You'll get a bit more stall out of the 350 converter. If you're talking about the 700R4, the answer is going to be no.... that uses a lockup converter, which will not interchange with the TH converter.
2 qts
yes a 350 turbo converter will fit a 400 turbo and vice versa
Yes
No.
No.
NO............
No it will not. Because it is a lock-up converter and the 350 turbo is not set up for a lock-up converter.
10 1/2 to 11 quarts
with torque converter and no transfer case (2wd) about 125 lbs.
remove the transmission and torque converter. Remove the bolts from the pump (front of transmission case) and remove the pump.
Between 12 and 13 qts.
I have an 81 with a 350 and I'm pretty sure from empty it takes 10 and 1/2 quarts.