Dr K. You were not losing your mind.
The Orange Hauler was constructed from a '62 Chevy pickup cab on a '55 Chevy passenger car frame.
I had the good fortune to hang out at Star Kustoms a little during the summer when Darryl was building the Ultra Truck (Monogram renamed it the Orange Hauler). I was surprised to see he was using a truck cab to build a custom, but even more surprised to see the finished product!!!
And, by the way, Starbird was a truly great man. He graciously tolerated a young teenager hanging around, contributing little although making every effort to stay out of the way, and even provided some narrative of what he was doing as he went. Had I more sense back then, I would have parlayed that into a part-time job, then full-time job, then career. Or at least, tried.