Boy does that look familiar.
I fully intended to rebuild mine when I bought it. It was an early 70's I think and had a swing-out galley, called a Swinger 6.
The lift system was cable operated with a winch and had to be repaired just to get it open. We were able to use it once then started disassembly to rebuild the top, water soaked and must have weighed 500 pounds by itself. The more siding that I took off the worse it got. Rotted sides, ends and floor. That's when it became a flatbed trailer. I kept all the electrics, they all worked.
I did grind off the back bumper mounts and if (when) I put the bumper back on I'll fit it up tight to the rear frame rail.
That side plate (curb side) that the step hangs on I ground off also. I brought my sides down over the frame, I thought it gave a more proportional look.
Good luck
Jack