I have a factory go wing on a 71 R/T. The decklids on the 70/71 cars had "cut-outs" in the decklid braces which located the support plates for the wing pedestals. Bolt the support plates to the braces and that gives you a template to locate the holes for the wing pedestals. The OP's pics do not show the cut-outs in the decklid braces (would not expect them on a 74), and I suspect the wing is not located in the right spot, and the pedestals being too far to the rear where the decklid radius begins and over-tightening trying to pull them down cracked them. My suggestion would be to find a 71 car which has the decklid cut-outs, measure them and duplicate them on your car, then get the pedestals and inner support plates and use the support plates as templates. You may have to repair some incorrect holes. Hope this helps, and good luck. Also note that these cut-outs are on some decklids which did not have go wings installed, so any 71 might have them to measure.