Consider the Fel-Pro Performance "Cork-Lam" valve cover gaskets, set #1646... double thickness (.313"), hi-grade cork rubber with a steel center core.... retains its shape and easy to remove/reinstall. Its the only ones I use... lifts the valve up slightly for better rocker arm clearance; seals great! As others have said, you may have to trim the gasket slightly as different covers/castings have different shapes.... I've had to do this with my cast aluminum Edelebrock small block valve covers. Also, consider using studs instead of the small short bolts... the studs are a positive locator... bolts can bottom out and not provide the proper clamp load. Cork-rubber always conforms better than just rubber. No need for any chemicals such as RTV (which you want to avoid unless only applied slightly to the cover.... and then dried 24 hours before clamping and running the engine.