Stock heads= Autolite 24's .035 gap
NGK 7773 .035 gap
Aluminum Heads = Autolite 3924's .035 gap
Motorcraft agsf32c's .035 gap
I know there are more plug choices than these, but these are some of the more common ones,or go to www.thecorral.net forums. Go to the power adder section and go into the nitrous section and there is a thread that is a sticky and it will show all types of plugs that can be used on different heads,modulars heads, heat ranges,etc.. Hope this helps.........