'84 Xtra-cab 4X4 frame rust

My frame rusted thru on pass. side behind cab. Junkyard said frame identical thru '95 and they had solid rear frame sections from newer trucks than mine for $150. Does anyone know if this is true? Anyway, after looking at my truck, the guy said he could patch it and not do the frame splice. As usual, once he got into it and removed the gas tank, it was more involved than originally anticipated. Now I'm PO'd I didn't trust my instinct and bought the frame section and had it done right on a frame machine. So after sinking too much $ into my truck, I noticed pass. side rear of bed is low. Probably moved before or during repair. Does anyone have any good ideas on how to shim this (1-2") and any experience on frame repair on 84-88 trucks? I know this is a long post but I really appreciate any help you guys can give.