1969 Dodge Dart Pro-Street 440

Ok need some help on this one. I and trying instal a wing but i cant seem to figure it out. I know that the thing hangs off the back of the trunk, but the wing is flat and the trunk is convex... How do i put a flat wing on a convex trunk???

I thought about shaving some of the center of the wing to follow the contour of the trunk, but i couldent make lines on my box ( my practis for cutting up the wing ) sweet enough to be confedent in cutting the real thing

Thoughts.