Ok, after a full can of wd-40, and 3 hrs. later we now know that the front 2 are '35 (4 1/4") and the 4 rear are '36 (4 3/4"). As for the rings it looks like 5 wheels have no visable slot when pressed up against the wheel, and 1 has an ELL shaped notch on the ring. As for using these on the truck, I can see that the wheel is riding on the studs and not the hub, but with the 10 hole retaining plate itself centers everything as well as the I.D. of this plate is the 4 1/4". I'm just curious how critical this is for the simple fact that this truck will undoubtedly see much calmer years ahead than it has over the last 70 yrs. If I do end up replacing these, does anyone know how hard these are to come by. Surely there must be alot of other trucks out there with maybe my wheels on them. Thanks for the input.