hey jim, welcome aboard. as a professional welder also i think you might like the mig better. tig will put a bit more heat into the panel than you want. also you wont need the penetration in the steel as with other things. while you can control the heat indeed it will likely be more time consuming and costly in the long run running with the tig. just a thought. know you have it and not the mig so it might b even steven. tig might need more finish work in the end because of the hear and possible warpage issues. even though you can produce a finer weld with the tig. you might relieve the stamping and distort the panel in doing so with the tig more so than the mig!!

also i have a 67 in the middle of restoration so if you need anything let me know. also take one panel at a time to fix. will take less time to complete it this way