[budsthe3]

My cylinder heads are casting: 3964291
I know these are for the 1970 LS6 454, the 375HP 396, and 427's.
But the date code on them is: B 5 71

If these casting numbers are for 1970 only, how can the date code be for 1971? I did notice the exhaust valves are 1.72, instead of 1.88

 

[EdCarpenter]

Over the counter purchase or warranty replacements.

 

[Ethan1]

Over the counter purchase or warranty replacements.

What I was thinking as well.:yes:

 

[zookpr]

427 replacement head and not an LS6 replacement head since they would have the 1.88 exhaust valves. I believe that the spark plugs are also different.