Are you just using the gasket or are you trying any sealant with it? I've heard the copper rtv works quite good(well?) on those flanges. I'd try it. It might get you by for awhile.
Years ago I had headers on the 340.
The flange was bent as yours
Straightened them best I could,
Used orange high temp RTV
Glued 2 gaskets together with it and sealed after any spots.
Worked.