I just flled a 31 5-window and used a panel from a older Monte Carlo. The contour was about as good as it was going to get. and you can also move the metal around after cutting it off the car by shrinking it to give it less of a crown if you need to
A buddy of mine has a coupe that the roof was filled with the hood from a 57 Chevy. The hood rockets were filled in and it looks good. It is the only one I have ever seen I think the hood from a 58-59 chevy truck would work out well and be easier to find They already have closed bulges in them.