I just envisioned some sort of lap joint with a heavy equipment like greased metal bushing or axel like joint at the bottom of the lap & an almost equally beefy lock pin in the top part of the lap. The driveshaft would need to hinge with a universal joint in the same plane as the frame hinge, possibly at the end of a remote mounted transfer case. A winch or hydraulics would slide the bed, but having the bed move on a single plane seems like less complication & a better failure mode when compaired to modern rollbacks.

Needing a shorter area to fit a truck in front of or behind a car & having a shallower slope when putting the car on the truck are valuable things, ramps are generally bad for both.

It's possible that it wouldn't work as well as I think, but it's definitely creative & interesting. Maybe just a solid frame with a properly designed air suspension that could drop the back & raise the front, squatting the truck on command, plus a sliding bed or ramps would work & be simpler 🤔 idk