I was wondering if anyone can help me identify a gm crate engine? I bought this engine two years ago that the guy claimed is a 10yr old "never been run" zz4. It has all of the carictoristics of a zz4. Aluminum angle plug heads, plastic timing chain cover, block says "hencho de Mexico" ect. But the problem I see is every ware I've read says the stamp on the block must say zz4 and mine does not. Here is the number stamped in mine on the block near the water pump in front of the right cylinder head. 1M1221-2P04. Can anyone decode this for me?