The OEM stock GM 12" torque converter from most th350's will do fine. It gives 2100 stall behind a 350cid motor and 2500 stall Behind a 454cid motor (higher engine torque). The 400sbc with the 12" th350 converter will stall right about in the middle of that range.
Some th350's came with a larger diameter low stall 13" torque converter. You want the 12" converter.
If your th350 has seen better days, yank it out and take it to a qualified transmission rebuilder shop. These are simple reliable transmissions usually don't cost much to rebuild/overhaul.
Qualified trans tech's do these trans with their eyes closed.
Adding a TransGo "shift kit" valve body upgrade/reprograming kit is a good idea while its being rebuilt.
The transmission shop will usually have these in stock.
If you don't have the right 12" torque converter the trans shop can get you a good remanufactured one also. Your application does not require a "high stall conveter".
You can save money by doing the transmission R&R yourself.
Last edited by F-BIRD'88; 03-07-2010 at 08:52 AM.