Damn, surely that was not originally a Utah truck? Looks like it came from up north or out east? Wow.
I seem to remember that after a certain year, Rangers had a 2 piece frame. Yours looks like it simply came apart as opposed to rusting off and breaking.... and usually the hangers & shackles go long before the frame does- looks like those are original to your truck, still riveted on.
I'd be really tempted to remove the spring hanger, inspect everything there (and on the other side) and if it's just broke off, plate & weld it and call it a day.
My buddy down the street has one of the old 3v powered F150's, maybe an 06? that looks pretty good, there is really no rot anywhere on the body and the frame is in super shape but the box crossmembers are totally rotted off. It's like they didn't even paint them or something.
Cab mounts are another problem on Super Duties, my rust belt ones look perfect and it's been either in NE or SD its whole life but my buddy in Texas had the ones on his '14 just totally fall apart. He didn't have to pull the interior apart to get the cab bolts out like I would have but I guess the threaded mounts on his style cab are well known for ripping out or rotting off... then you're really in a pickle.