the th350 shaft is a different length. If you still need one measure from center to center and call up Muscle motorsports and you will get one from them (after looking I think they are calling theirselves musclemotorparts now) anyway here is their link
http://musclemotorparts.com/index.html
they get used nascar parts and sell them. reasonably priced. if you are using the stock 10 bolt in back you will need a conversion U joint if you are using a 9" then you don't need to do anything other than install it.