There's really no particular reason the shape needs to match the original. Referring to the diagram above I just cut a rectangle of dimensions A x D, then cut a smaller rectangle out of the center so that the foam was 1" wide around.

 

Very true! Dimensions on this are not at all critical.

I still think its very useful to have the full dimensions, as these cars become more collectable and people want to keep it as original and correct as possible. They can fab a version of the part true to the original.

 

Yes, you are correct, but I just enjoy trying to keep things as true as possible, and maybe making some
slight improvements in the process.