C3 LS5 Heads/Intake

[jim34671]

I have a matching set of bare heads that I'm trying to depict dates and applicability.
There are 3964290 heads dated G29 9 and G7 9.
My understanding was that 4290's are 1970 heads and not 69.
If they are month coded G,would that mean July 69?
Did GM cut heads for 1970 that early in 69?
Did the strike affect this?
The matching low rise intake 3855287 is also dated J27 9.
Would these be correct on a very early Jan production Corvette?
Thx
Jim

[Joe L.]

Re: C3 LS5 Heads/Intake

Jim------

Generally speaking, the GM #3964290 heads are 1970 heads which were used across the Chevrolet car lines for oval port, big block applications. However, some of these head castings could have been used for late 1969. If so, they will be machined for gasket type spark plugs. If they are machined for tapered seat spark plugs, as most if not all will be, then they are 1970 heads.

Although the 1970 model year for Corvettes did not begin until January, 1970, the model year for most other Chevrolets began at the normal time in September. So, if these are 1970 heads as confirmed by the spark plug machining, they were likley installed on an early 1970 Chevrolet model other than a Corvette.

I believe that the casting number for the manifold should be 3955287. This manifold was used across the Chevrolet line for the 1970 model year for big block, oval port applications. It was NOT used for any 1969 Corvettes although it's remotely possible that it may have been used for another 1969 big block application late in the model year.

Given the NCRS/NCCB "6 month rule", these heads and manifold would be "correct" for an early January, 1970-build Corvette. Just barely, though. While correct by rule, it's very unlikely that heads with these dates would have been actually used on such a Corvette.