..with all metal gaskets you should use wrc long stud or at the very least a arp stud/nut kit...you require a greater clamp.
My 600bhp lump runs WRC long stud and cometic gasket
My DIY engine runs WRC long stud and WRC gasket (500bhp)
My runaround runs a Grp A and wire rung block (350bhp)
Fuck coopers rings right off