Mark - my block has the same casting number as yours, but my head has a different casting number. Also, on my head there is a large number 2 (presumably instead of 7 or 9) cast not below the GM symbol but nearby on top of the head under the valve cover.
Ya I have seen the GM number up to 14 on some of the different heads I have looked over. It would be nice to know their meaning.
There are also some numbers on the plug side of the head between plug 3&4 where mine has:
11
499
The one I am looking at is:
X8
12
499
Any idea what those numbers mean
Mark
