Seadog,
If you bought new rims is it too late to return and get proper offset? Another solution is spacers come in many width sizes can you go to slimmer size? If can't return see below.

My chev is a 49 suburban but I am currently building a 46 Dodge on an 83 el camino frame. I bought some 15" rally style chev wheels at a swap meet and had to put in 1" spacers to keep tire from hitting frame due to the offset. Tires are "centered" width wiase in fender. I built a 1" square tube frame with enough height to make the floor level of bedsides sit on the "arch" of the rear kickup where the floor originally was. Then you can bolt/attach the bedsides to the tube frame at whatever height looks right to you. You will lose about 4-6" of depth in the bed doing this but my dodge will be a grocery getter and not a hauler. Hope this make sense as another way of solving your issues.

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