Hi- I have a 1974 F350 Super Camper Special Regular cab. It is the 10K GVWR and has the 70 Dana axle. It has the stock dog dish hubcaps but I recently bought a set of the 15" full wheel covers that were optional on this truck (as well as other years). I also bought the full set of the "reducer rings" or trim rings that are necessary to adapt these 15" Ford wheel covers to fit on the 16" rims. I can't seem to fit these onto my truck? I assume that with my F350, it probably came with the 9.50-16.5" tires up front and the big "super singles" (12.00-16.5" I think) rears and the original owner swapped them out sometime during it's history to Ford 8 lug 16" rims. My 74 Ford Truck sales brochure shows these wheel covers as optional and they do refer to them as the 15" and also refer to the fact that they will fit the "16 1/2 inch" wheels. I believe that the current rims are 16" x either 6" or 7". Do I need different rims or will they only fit the 16.5" rims? What am I doing wrong? Thanks.?