I used a set of napa ultra seal header gasket and the high temp copper rtv

on both sides of gasket and letting it hang on a wire for 15 mins to cure some

instaled the gasket and header bolts just snuged up some,let sit over night,torqued the bolts down tight by hand

no leaks for about 3 yrs till I pulled the engine

this was a used set of headers and pitted on the flange and warped some

I used a flat file and smoothed the flange flat around the port

68 Dart 318 A body 73 k-frame...

I know what ya mean on tight fit and header leaks

I also removed the studs in the heads for ease of installation

good luck