The clamp rings are recommended. I'd even say required.
I expect the wheel is really supposed to use a 9/16" wheel studs.
With the clamp plates that use a beveled lugnut I bet you can find a 1/2" lugnut that will correctly fit the seat/bevel in the clamp plates, it'll probably have a larger than usual hex.
If you don't like that method your next choice is press out the original wheel studs and press in new 9/16" ones, and likely have to bore the holes in hub and drum larger to fit an available 9/16" stud. Might get lucky and find a direct replacement, all depends on the size of the knurled shank and what you can find.
