question on matching head numbers
 

I found a set of heads that match the casting number I need except it has an x at the end of it. Is this still a legal head? What does the x mean?

NHRA/GM allowable casting numbers:

3998991 or 3986339

found a set with 3986339x

thanks,

Re: question on matching head numbers
 

3986339---1.72 intake/1.5 exhaust-74CC--- 68-69 307 eng

3986339X--SAME SPECS(int/ex/cc)---71 307/350 eng

3998991---1.72 intake/1.5 exhaust--75CC ---68-69 307 eng
72-73 307/350 eng

hope this helps--Comp387