Those look fantastic! Love those between-the-wars designs and color schemes. I once got to see some, if not the same, very similar, ones flying at the Planes of Fame museum in Chino, California. They are LOUD!

Certainly an interesting challenge - and may not be any easier than 3d printing!

The only thing that has me stumped is the outer lip that seems to go up much higher than the detail in the middle. That might indicate a need to make a negative mold, so scribing the rings and the center dimple might be the way to go.

That is great! For what it is worth, I would probably find some tubing and/or rod in diminishing diameters around the size of the ribs, then wrap wire around them, cut off a loop, and solder or super glue the end together, then glue them to a base.

If you have access to a vacuum forming machine, that might be the best bet. Probably not that hard to come up with a master either, some kind of dimple for the middle, and then some concentric rings. It would also be close to scale thickness.

Just a heads up, the hedge cutter was never used operationally on Cromwells. The existing pictures are of a prototype that only appeared once the Normandy campaign was over.