What is the 700R4 found in OEM?
Most GM rear drive vehicles staring about 1984 until it was supersceded by the 4L60 (which is really the same transmission) in the 90's and the 4L60e which is similar but requires a computer to shift.
You don't want a transmission that was behind a V-6. The smaller V-6 has a different bell housing pattern than your 350 and the stronger parts may not be in one from a larger V-6.
If you get one from a four-wheel-drive you'll need to change the output shaft and tail shaft to a two-wheel-drive type.
If you get one from a Corvette you'll have to change the tail shaft to one with a conventional mount pad.
