I know what you are looking for as I have a set of the 20's on my 55 1.5 ton. Though it may be cheap to have one cut out the center of a wheel, Id also recommend maybe contacting someone on ebay? to cut what you need from a new piece of steel. I had a large (16"?) stainless disc cut by someone on ebay to match the hub of a 2004 gmc envoy. It was used in a custom electric chopper build. With having one custom cut, you can identify the center bore size, the 10 on 7.25 bolt pattern and potentially add the OD of the disc maybe? in order to help center it etc on the wheel you want to convert. Or some other means of making it centered. Either way, I do know that I have axles and wheels from a 94' chevy C3500HD (HD being the key part) that has the same 10 x 7.25 bolt pattern but i believe the center bore is diff. maybe another route to look at. good luck and happy hunting.
