The engine is out and sitting on my engine stand.
![Very Happy :D](./images/smilies/icon_biggrin.gif)
When I pulled the flywheel off, I discovered that the block had an X and an I scratched into the cylinder bank castings. Having read that the X may refer to a higher nickel content in the block, I decided to find the casting number out of curiosity to see if it told me anything, but it doesn't have one. Some time searching the Internet gave me some answers...
According to multiple sources, my engine is built around a service block based on the fact that it has no casting number. I found only one reference to an I block in a discussion of the service replacement blocks. I could not confirm that the X refers to a higher nickel content, but there seems to be a notion that they may be more desirable. I pulled the center freeze plug and did the drill bit test. I found a 14/64" bit shank fit snugly between the bore castings. Everything I find on that seems to say that the block was cast with the casting molds used for the 428, some 361,391 and 406 blocks. While the floor of the water jacket has a number cast into it, its 352 instead of the magic 428.
So what do I now know that I didn't before? I should have a block that will easily handle a 0.030 overbore without any trouble. Any further judgements will have to wait until after I can measure the bore & stroke.