That's why I suggested to the Nova owner to follow your advice...I still feel he needs to square the sub-frame to the body compared to relying on rear frame points as well (wouldn't you agree, he needs a starting point to hang sheet metal?). The rear frame, in the state it's in now is a misnomer when it comes to lining up the front and sheet metal...Wheel base is also not a measuring point any more because the rear frame rails...When the rear differential is installed, it may be off to one side, to check, measure gaps and cross measure points on the rear of the car, with his O to J measurements being 3/16 of an inch difference, he can expect his rear end to be out by 3/4 to 1 inch or more on the ends of the brake drums. This won't affect his front sheet metal alignment.
So I feel he should get the front sub-square to the body, not the rear frame rails and do as you suggested by starting with aligning the rad support and hanging sheet metal, all the while, some adjustments are going to be constantly made to the front Sub-frame to adjustment for gaps and fit.
The rear quarters and some of the floor have been replaced, the rear frame rails aren't moving anymore with these items welded in or more problems arise...This way he can get a weekend driver with fit and gaps that hopefully he can live with.
I'm rereading my post and your post and I think we agree, just used different words.