I think the shafts are the same, as the trans length is the same, and the splines should be too
only difference is the floor pan that covers the trans is flat for a 3spd and has a hump for the 4spd - your 3spd pan won't go on over a 4spd - should be able to find one tho as the 4 speeds were at least as common as 3's, maybe more
Bill
