So you base the frame rail location on the body work that was hit or wasn’t there, or the body work locations on the frame rail dimensions that are published?
A little of both. The tolerances on those cars isn't all that great. If you can make things line up to where the chassis dimensions say, that's step one but aftermarket panels aren't perfect and often times need massaging for a good fit. So just doing the inner structure isn't always going to work out perfectly.
My car, a 70 Barracuda Vert is a mess. Not as bad a that AAR, mostly just rust, but a LOT is getting replaced when I get started. I built a beast of a universal jig for it and any other cars I might put on it later. Once I get things locked in place, it's not moving. Nothing will get welded together without mock up of some sort. One section at a time.
