Ron;
Here's another suggestion. I had the same problem with my header flanges. I asked a couple of circle track stock car builders and they recommended using "stove bolts." They also said to use locking nuts if necessary. I got the stove bolts from a local nut & bolt supplier and used them without the locking nuts. That was about 8 months ago and everything is still tight. I used the doughnut type gasket.
Rodger
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