As stated above, don't worry so much about the dims. Instead you might want to try to get the hood and doors to fit before you start taking the panels apart. With the cab on the frame use the existing holes in the firewall and screw(lag bolts) a 2x4 or two on to the engine side of the firewall. Use a jack to raise the firewall and thus the floor to help align the panels. Once the panels "look about right weld in some electical conduit at the door jambs, firewall to cab back, and side to side. There, your cab is now within specs
