Heil built a gravel bucket like that, but so did many other manufacturers. Wheels are not easy to find. You need 54 and older. Later have the same bolt pattern, but the hole is 1/2" bigger and they pilot on the hub. About all you can do is look at the wheels. If they have some sort of lock ring assembly, they are ok. The RH5° split in the middle. If the lock ring is visible on the steering axle, they are ok, if not they are the RH5°.
