It's the reverse of that Chris. With the steels you have to take the bump out so the drums more flat like a '40. The thing you are looking for is more like a giant fender washer. The ring for wire wheels puts it onto a '40 drum to support the middle. Look at a model A-'36 drum and a '40 it'll click for you.
Tim
Chris,
I have a set I got from Antique Auto/P.S.I. years ago. The problem I had was that when the ring is in place the wheel is spaced out a bit more and the lug nuts don't engage enough of the threads on the studs. This was on my '33 Woodie. Maybe some studs are longer?
Al