i have a pair of prc aftermarket casting ls3 heads that i know take a 3/4 reach plug, what are you guys running for plugs, twin turbo 408 20 psi, i ran the tr6 and 7s with my 317 heads but those are like a .708 reach plug i beleive, this will be on pump gas and occational race fuel, my old combo liked the projected tip plugs tr6