The originals I think were 36" from mounting point to mounting point. The reproductions were 3/4" closer together. At least it was that way until a few years ago when FPAP started doing a correct reproduction. My 70 'Cuda is an original wing car that the wing was taken off of. The holes are welded up on the decklid. The second owner installed a repro wing on it and the holes are inboard of the originals. I have toyed with putting a real wing back on it but have just never done it.
Arno