If you will eventually be putting in a torquey 351, you might want to put in a stronger tranny than a t-5. It costs more to do the tranny twice(once now, and then again with the 351) than it does to buy a beefier one to begin with. Also, the Tremecs come out of the stock floor hole, and they should fit a car designed to a c-6 like your '70 pretty easily. Ask around a little before you buy (which is what your doing here I guess).