Measure twice, tack weld/clamp once, measure again. Measure straight back. crossways from the opposite side, and from the floor to the frame mount AND the top of the core (use a level on the floor AND the truck first) My body is sitting on a "frame" I built to hold it while I'm restoring it (like a rotisserie but doesn't rotate) After measuring I also mounted alignment points on the "frame". Measure everything from the firewall. Mine looked beautiful when I bought it but during disassembly I discovered it had a small hit in the front that had a cheap sloppy repair. They obviously just pulled the core out with a come-along and welded the crack in it. When I pulled the front sheet metal apart, the inner Apron on one side was also buckled. When I measured from the firewall to the core that side was off by about 1/2 inch and the frame mounting point was 3/4 inch higher on that side than the other side. I also measured the fenders and hood and checked against the core to firewall. Tack/clamp, hang the fenders/hood/grill with a few bolts like GlassPony said, and adjust accordingly. Good luck!