Place I buy some aluminum outers from (and who also make steel ones) is just making some 20" steel wheels to use a Chevy ralley cap. They had some solid centers made up and cut the windows in it to look like a ralley.

They weight a TON.. (but it's what the customer wanted which is why they did it)

Oh, and the proportions do look odd as well with the small center cap in the middle of such a large area.

My 18" x 10" aluminum wheels only are around 19 pounds each, I think I will stick with that over tank wheels.