Woodz428,
Here is an interesting link:
http://www.428cobrajet.com/id-block.html
Point taken...I will have to do the drill bit test and do the math and put this to rest. Tomorrow.
In my block, 352 is stamped inside the water jacket. On the outside of my block is a casting number C6ME-
Yes, it has a dash, but nothing following. That's a bit odd, except when you consider that the 352, 390, and 428 all carried C6ME-A as a possibility, but only the 390 and 428 shared the C6ME designation (i have not checked other block sizes.) Looks like the "A" was ground off to minimize (or maximize) confusion here.
I would assume that by puting a block number in the water jacket, it would make it easier to identify and harder to falsify (grind off)
Take the test yourself and tell us what you find
I really want to know if you see it.
Mike