1970 Spoilered deck lid?

[jreynolds 10]

I am restoring a 1970 Mustang coupe, I really like the spoilered trunk lid with the extionsions, however, when I called one of the places that sells the item, they say it takes a lot of fiberglass work because they make the part without the trunk weatherstripping, so when you install the weatherstripping in the trunk the long middle "fin" sticks up a quarter inch taller than the extensions on the side, can anyone help?