Maybe a set of the 5.0 Mustang GT heads..... You'd have to do a bit of research to find the heads with the right cc's so you don't bump the compression too high..... or, if you don't drive it a whole lot maybe the 69 heads with a bit of lead substitute in the fuel tank???? Might also want to consider a set of the late model GT 40 heads, just not sure what all they came on. Guess I'm just spoiled, I just pop the big bucks for the aluminum aftermarket heads!!!!!