68 Numbers Mystery - build date, VIN, heads

[Gary K.]

1968 convertible VIN194678S411574, which indicates February 1968 by monthly production numbers. Trim Plate has date code C16 which is October 1967. Block not original, but heads we believe are original to the car along with distributor, alternator, valve covers, etc - head castings are 3904391 Hi-Perf GM3T date D11 7 which I think indicates November 1967. Car has been in family since 1969, my Dad confirms originally 3x2 435hp car and he describes the car as a "67 and 1/2" because it was an early 1968. I know what has been done to the car and who did it and when. I don't think trim tags, vin numbers or castings have been modified at all.

Here's the question: these -391 heads are supposed to be for a '67, were there late year production heads with D11 7 that could have gone in an early '68? Trim plate Oct.16 '67 is before the D11 7 heads - would this work? And my biggest mystery - the VIN number, indicating February 1968 which doesn't work with the other numbers. As I start really getting into this car I want to do things right and need good info - Any help much appreciated!!

[Joe L.]

Re: 68 Numbers Mystery - build date, VIN, heads

1968 convertible VIN194678S411574, which indicates February 1968 by monthly production numbers. Trim Plate has date code C16 which is October 1967. Block not original, but heads we believe are original to the car along with distributor, alternator, valve covers, etc - head castings are 3904391 Hi-Perf GM3T date D11 7 which I think indicates November 1967. Car has been in family since 1969, my Dad confirms originally 3x2 435hp car and he describes the car as a "67 and 1/2" because it was an early 1968. I know what has been done to the car and who did it and when. I don't think trim tags, vin numbers or castings have been modified at all.

Here's the question: these -391 heads are supposed to be for a '67, were there late year production heads with D11 7 that could have gone in an early '68? Trim plate Oct.16 '67 is before the D11 7 heads - would this work? And my biggest mystery - the VIN number, indicating February 1968 which doesn't work with the other numbers. As I start really getting into this car I want to do things right and need good info - Any help much appreciated!!

Gary------


First of all, D 11 7 denotes heads cast on April 11, 1967. Under NCRS guidelines, these heads would be slightly out of the window of acceptability for a 1968 built on October 16, 1967 assuming that 3904391 heads were acceptable, at all, for a 1968. The NCRS guidelines are "generous" in most cases and it's really unlikely that an October-built 1968 would have an engine with heads cast in April-----not impossible but unlikely.

Beyond that, the GM casting #3904391 cylinder heads are heads used for 1967. I have no information that they were used for 1968 and it's very unlikely that they were. For one thing, the 3904391 heads do not have temperature sending unit bosses. 1968 engines used head-mounted temperature sending units.

The discrepancy between the VIN sequence number and the body build is hard to explain. It's very unlikely that a Corvette body sat around for 5 months before it was used to build up a car. Impossible? No, I don't think it's impossible to have occurred for some weird reason but very, very unlikely.

Considering all of the above questions, I would say it is VERY unlikely that this car is legit regardless of whether it's been in the family for 42 years. Somewhere along the line someone has forgotten something regarding its history.

[Tom H.]

Re: 68 Numbers Mystery - build date, VIN, heads

Gary !

Just for fun............... re examine that trim tag and see if that C might not really be a G. Just a thought.

[Ralph S.]

Re: 68 Numbers Mystery - build date, VIN, heads

I should be G16

[Reba W.]

Re: 68 Numbers Mystery - build date, VIN, heads

I have judged many cars which where we first read a "G" as "C." There is a statement about that in both the 1968-69 and 1970-72 judging guides.

[Patrick B.]

Re: 68 Numbers Mystery - build date, VIN, heads

The 391 heads would not have appeared on even a very early 68. They were discontinued in May 67, and late 67 435's started using 840 heads with the temp sender bosses cast in but not drilled and tapped. Since the 391 heads had no provision for a temp sender they could not be used operationally with a 68 manifold, and the taller 67 manifold would not work with the 68 hood. Regardless of any 6 month rules a 68 435 could not be built without 840 heads.

[Gary K.]

Re: 68 Numbers Mystery Solved!

The "C" is a "G" 16 which solves my VIN versus trim tag mystery, Thanks!!!

For the 3904391 Heads the mystery remains. Motor was swapped out in early 70's with the CE series casting 3999289. It is at that time I assume the Tri-power was unfortunately taken off and replaced with Winters intake and a huge Holley 4bbl. Other than that most everything seems to check out - exhaust manifolds, distributor, valve covers, etc from the '68 model year.

If the -391 heads simply do not work date-wise I guess the original motor could have been swapped out with it;s '68 heads, then the mechanics doing the work in early 70's scrambled around to find some Corvette appropriate heads and came up with the desireable -391's. This car is a driver, I'm actually thrilled to have these heads. Now I have to decide whether to find a date-appropriate '68 block and tripower setup.

Thanks for the assistance....