On the head bolts boss’s, when I go thru I use a bead of Permatex (The Right Stuff Gasket maker). I make a bead below the washer, around the bolt, so when installed it makes a sealing plug. Just a bead, if you use to much it is hard to get the bolts out. Let it dry or it won’t seal. If I use a copper sleeve I epoxy it in. I have only used copper on the pushrods though.
https://www.summitracing.com/parts/ptx-34328