Help please. Bed alignment issue.

[SunSoaked]

Thanks. I located the 8 bolts last night. Fortunately, the PO did a frame off resto before losing interest and throwing it all back together to get rid of it. One of the reasons I bought the truck was because it was a 100% rust free Arizona vehicle with a freshly sandblasted and painted frame and undercarriage.
Every nut and bolt on the chassis is brand new and shiney still.
I could see that the nuts and washers had room for back and forth adjustment because I could see space in the frame slots.
Tonight I am going to loosen the 8 nuts and then try to align the bed and cab and get it centered on the thrust line. Then, hopefully, I can shim things vertically.