1960 was the last year for the torque tube.
It's always kind of scary when you are trying to buy parts from someone who has no clue about what he is selling. The output shaft housing on a stock 57 transmission is longer than yours, so if your guy still has a torque tube the owner before him may have already swapped the output shaft and housing. If he has open drive, you already have the parts you need on your present transmission (assuming he has a Dynaflow). The only way to tell for sure is to crawl under and take a look.
Also, the block holes for the engine mounts are different between 56 and 57, so try to talk the guy into giving you all the parts between the block and the frame. He won't be needing them if he is going to install a Chevy engine. Lastly, just in case the guy is totally F'ed up and doesn't even have a 364, measure across the front intake manifold bolts on your engine and his. The 364 manifold is wider than the 322.
Good luck, and please let us know what you find out,