I've been to every Chrysler Nationals at Carlisle since the first in 1991. I saw your car there in the 1990s when I would drive in from Chicago in my 1962 and 1966 Imperials. The past owner had to be the guy you got it from, attorney in the Philadelphia area. Met him at a local show in 2018 when I still had my red '69 Track Pak GTX; he was only in town because his daughter had a swim meet at Penn State that weekend. I remember the mileage, and the guy told me he let it go because he never drove it. My first car went to Edgarton, Ohio in 1981, and changed hands through a dealer about ten years later. I have no idea where it went from there. It has been in Roger Wilson's 1970 GTX registry for years, with no information surfacing. Picture below from my honeymoon in 1977, car was completely stock original. Still have the wife, 44 years later. This hobby is a fairly small and tight group, you never know when you might get a good lead.
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