Tom, My saff runs arp stud and nut i used a cometic 3 layer gasket but it was the early type and failed..

So i now use GRP A gaskets due to them being cheaper
cos imo re-useable ones cannot be re-used

Cometic gaskets are good cos there thicker and drop the comp ratio a little

i've been advised that when running big boost on std head bolts re-new the bolts one at a time after 6k you will have no probs