Now that I had measurements, I could cut out the firewall and front floor section and make it all work. I wanted to use all the wiring, heat/ac and dash from the GMC. I wanted to use everything in case we have problems out on the road, I can give the vin for the GMC and they could order the correct parts to fix it.
I made the center section of the floor the same width as the engine so it could be removed to work on the engine. The engine ended up completely under the floor
At this point I hoped it would all fit because I had no way of sitting the cab on the chassis to test fit. the first time it was set on the chassis was after it was painted.