Got my heads back from the machine shop today and had them tank the manifold as well.
Underside of my manifold has a pan riveted to it and appears to have a good amount of crap and such built up between this pan and the under side of the manifold.
Should I be removing this pan to clean whats built up by drilling out the rivets or am I ok just leaving it as is?

Thanks
Tbruz

 

That is a heat shield. If you can pry rivets out and take pan off and clean would be better. If you drill do not go thru the manifold into runner or you will have a leak.