Gary,
Not sure what year Cadillac you saw, but that was pretty common in the 60s.
Remember, no such thing as our towing machine trucks back then. A pickup was a lightweight frame, narrow tired, and often had rear coil springs with a wood bed. Power packages were 6-cyl engines or tiny V-8s (283ci, 252ci) backed by 3-speed transmissions or the old clunky 5-speed top loader. They were manure haulers more than anything.
Now a
Cadillac or
Oldsmobile - Wow. Now we're talking heavy X frame chassis with larger wheels and tires than a pickup, huge 472ci or even a 500ci V-8 with a heavy duty automatic transmission. Plus power steering, air conditioning, and a radio! The Cadillac and Oldsmobile were the favorite chassis for ambulances and hearses, and some motorhome manufacturers actually used Cadillac chassis and front ends from the factory, even though a lot were home made.
Not sure if it was suitable for a 5th wheel trailer, but the TV of choice back then was the family sedan, not the farm truck out back.