Back in the old days. Vehicles whether heavy truck, car or buggy were built on a chassis. The chassis had the springs, suspension, wheels, engine etc. Then the body was dropped on.
It's not a brand thing, it's a design thing. If you built a go cart or a lawn mower engine propelled car as a kid it probably went like this: Built a chassis with wheels, bolt the old lawn mower engine on the back. For a cool looking car you put on a body!
The 58 T-Bird and amazingly the 37 Zephyr (Lincoln) were unibody structure. Later the Mustang was unibody.
Can't do a frame off resto on a unibody. The body is the frame!
Most "modern" vehicles are unit construction. Crawl under your 2000+ vehicle and see if you can find the separate frame/chassis.
My '64 1/2 vert. Ordered May '64. D code 4 speed, handling package, caspian blue, accent group, Ford blue manual top.
'68 vert. driver. Owned since Apr '78. C code AT, AC, PS, P disc B, PT lime gold, standard black interior and top. NOS RF fender and left quarter.New top and folding glass.