I can sympathize. One thing I will say that I learned many years ago from a friend who owned a body shop/repairables business, and who helped me with my FE Mustang when I first got it - he taught me that these cars ( and other brands too ) will suffer from the shock towers sagging inward with age, even on rust free cars. A lot of times the issues people have with header bolts to shock tower clearance, that can be part of the issue. We had some other front end sheet metal work to do on my car from accident damage, but at the time he also put my car on the Kansas Jack frame device, and pulled the shock towers out considerably to get them back into spec. Using the combination of an original Ford heavy gauge export brace, and a Monte Carlo bar, seems to have stabilized the issue, and it hasn’t changed since. There are frame and engine compartment dimensions, diagrams, and reference points, in the Ford Shop Manuals. I would advise anyone to check those dimensions when they get a chance, sometimes it will explain the issue.