Be sure to swap the regulator from the Cadillac as well. The Caddy will probably have a higher-amperage generator than the GMC, which is a good thing, but in order to make use of the higher capacity, the corresponding regulator must be used, or your original regulator would have to be reset to the higher amp rating. The Cadillac generator will probably have ball bearings front and rear and it will probably be longer from end to end, so some tinkering with the GMC bracket might be necessary. I usually use a short section of 1/4" pipe as a spacer, with a longer bolt on one end.
Someone who is skilled with a TIG welder can fix those broken end frames, so don't discard them.
Jerry
