This is a very common problem with these cars, which is why the aftermarket fix came out. Never tried the portapower trick but in the old days it was not uncommon for the front end shops to fix this by chaining down the sides of the frame and jacking up in the middle to do the same thing. Don't see why a good front end shop couldn't still do this.after fifty years these babies sag in the middle but once it's put back in place your alignment problems are gone.
Just to add my two cents worth, if at any time you have the front end clear of everything, check the measurements across the frame at the point where the upper control arms mount and if it doesn't match factory specs. put a ten ton porta-power across the frame at that point and push it out until it springs back to factory specs, after fifty years these babies sag in the middle but once it's put back in place your alignment problems are gone.