Ben,
I just got married. Take my advice - sell the car, and save yourself a lot of aggrevation.

I've had success welding cracked headers before, but it depends on what shape the material is in. I would recommend welding a patch, and then use a gas torch to anneal the area (heat it to a dark, dark cherry, and then slowly reduce the heat and let it air cool). This process should delay the onset of a crack near the weld. Good Luck (with both the wedding and the header!)

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Dave Youngren
NER ITA RX7 #61