I had a leaky manifold on my '75 300 6 cyl. and I've removed the intake/exhaust manifold, cleaned it and the block up real good, and and have the new gasket. Some folks say to use permatex copper and some say no. And if I was to use it, would I put a bead on both sides of the gasket (that is, the block and the manifolds), or just one side? Any advice appreciated. Thanks

 

any manifold should seal with good gaskets but i have had that problem with 460 exaust manifolds in the past take them to a machine shop and have them checked for straightness and ground flat if need be then you should not need any thing more than the gaskit its self

 

Just my preference...but I put sealer on every mating surface possible.

 

I use these brand of gaskets for my 351M with headers and have had great results.

Header Gaskets 300 6 Cyl 66-86

Header Gaskets 300 6 Cyl 66-86 CLOSE OUT

My mechanic buddy uses copper permatex on all exhaust gaskets....