The plugs that came in my crate motor are AGSF 32C. Crossed to Autolite thats 104. Looking though a search everyone uses Autolite 3924. The difference in the plugs is that mine are tappered, have a .708 reach and a heat rating of D14. The 3924 uses a gasket, has a .75 reach and are a heat rating of D11. The main difference I'm worried about is the gasket/tappered. I heard alluminum heads needed a gasket, not a tapper??? What should I go with?