As for factory, that I don’t know. Perhaps it was a dealer installed thing. But, I do know a fellow that has his pickup box mounted on a dump system like yours. The box is mounted to the lift frame. The rear of the truck frame is shortened to accommodate the box when it pivots. The frame is shortened to the first crossmember from the back. The rear fenders are not bolted to the running boards either.it is pretty slick. The box does ride a tiny bit higher than normal and it is discernible.

Last edited by Fox; 10/31/2020 3:51 AM.

1970 Chevrolet C10
Grandpa's -- My first truck -- In progress to shiny
Follow the build in the Project Journal
1950 Chevrolet 1-Ton Dually
"Ole Red Girl"
In the Stovebolt Gallery
More pictures here
1951 GMC 9430 1 ton dually--Shiny! | 1972 Chevrolet C20- Rusty- the puzzle box lid for the C10 | 1962 AMC Rambler American- my wife's
Parts trucks-
1951 GMC 9300 | 1951-GMC 9430 | 1951- Chevrolet 1300