My 05E Norwood '69 Z28 has a pair of the 3927186 cylinder heads on its engine and both heads have the bosses and 3 drilled/tapped holes for a right side alternator mounting location that was adopted for the start of the '69 model year. Right side head has a casting date code of E79 (May 7, '69). Left side head date code looks much more like E78 (May 7, '68) than it does E79 -- see photos. The engine build date per my P-O-P is 0513 (May 13th).
Has anyone observed a 3927186 head with a casting date as early as May 7 of 1968?
It does look like an 8 for the year, but I'd say it is actually a 9 vs an 8. The odds of getting a head exactly one year off the other is pretty slim, and I don't think the 186 casting came out until '69, anyhow. I could be wrong on that, thoguh.
I vote 9 on both heads too
8s and 9s often look alike with castings. Yours are 9s. I don't think they were being cast in May 1968.
We did this report on cylinder heads a while back.
https://www.camaros.org/cylinderheads.shtml
Encouraging info -- thanks to all who responded. A friend took my question to a Corvette forum and received very similar responses to those here.
What about the possibility of the new-for-1969 head casting p/n 3927186 being introduced early, as a running change during the last 3-4 months of the '68 model year? If introduced early, and if Flint didn't spend tooling $'s for drilling/tapping the alternator mounting holes, were these new head castings ever used on later '68 engines with their left side alternator mounting provision remaining in place until the actual 1969 start of production, when the change over to the right side alternator location took place?
If that is unlikely (or never documented by anyone in CRG as having taken place on an engine), I would have to agree it is most likely explained by a digit that got "buggered up" a bit during the mold making/casting process.
The days of the year are the same. They are both May 1969 castings. My advice, accept that both are original. The preponderance of the evidence suggests both are original to the engine. No need to prove otherwise. These are SAND castings, so they aren't always perfect.
Test castings would have M dates.
"There is one exception to the normal casting date convention. When the foundry was evaluating a casting process change, the foundries used special codes to indentify the test parts. Evaluation castings made at Flint received an M month code and evaluation castings at Tonawanda would typically have an X cast on the part. After evaluating the parts, the heads would either be destroyed or released into production. There is no way to determine the date an "M"-coded part was poured."