Made it. Home Depot sells like two foot square sheet metal. That's why I posted the drawing for anyone else to use as a guide. Getting those arcs right can be difficult. I always had trouble getting that handle set into the screw and thought, there could be worse places I could be trying to get my spare down than my driveway.
This was exactly what went through my head when I tried for god knows how long to get that thing down when I had to change a tire. That's why I didn't put it back up there. This is a very handy mod, thanks for posting it!