For AD (47-54) trucks, according to the FAM, distance between front spring eyes on the frame are the same on 1/2 and 3/4 ton, but the rear springs are actually longer on the 1/2 ton (~52") than the 3/4 ton (~44"), and according to the GM specs, the 3/4 ton frame is deeper (vertical dimension) and also thicker (3/16" versus 9/64"). The 3/4 ton rear springs are wider (2") than the 1/2 ton rear springs (1-3/4").
