There was absolutely no difference in the way the frames were built. However, the big block equipped cars seemed to settle the frames a little bit more over the years resulting in the upper control arms being pulled slightly inward. This is generally resolved in using the offset upper control arms which restore the camber adjustment. In severe cases I have heard of cars going back on the frame machine to be pulled back, but if this was necessary I would use it as an excuse to buy new tubular control arms.
1965 Impala SS 396