I built custom trailer hitches for many years. It might be simpler to fabricate one from channel iron and square tubing than to try to adapt something already assembled.

My method was to make a pair of side rails about 12"-18" long from 3" channel iron, with a cross piece of the same material, then cut a square hole in the center the right size to accept a receiver tube. Then the receiver tube is welded and gusseted into place with triangular 1/4" plate on both sides, top and bottom. The whole assembly can be bolted on, using 5/8" Grade 8 bolts. If an under-bed spare tire is involved, it might be necessary to adapt the spare tire carrier somewhat.
Jerry

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