Well IMO the 5 speed that was behind the V-6 is going to be way to light duty to live long behind a 350, especially if you plan to pound on it a bit..... I would recomend a 5 or 6 speed out of a V-8 car, Vette or Camaro, or plunk down the $$$$$ for a TKO... Lot of work and expense for a tranny that will probably not live long.

As for the Saginaw........ Well, IMO they're junk. Fairly heavy duty but almost impossible to make it a smooth and quick shifting unit. Tried to make one work for a guy once, hopeless cause. He eventually found a Super T-10...