It's definitely a gen VI block. It's got the aluminum timing cover with 6 bolts and the smaller freeze plugs. However the block number is a mystery as I can't find it on any database. It's 12561359 and the casting is crystal clear so the 9 is not a poorly stamped 8. I've already asked several sources about this and all anyone can say is that towards the end of the manufacturing run for these engines GM did a very poor job at keeping records. It's got a hydraulic cam and lifter setup with a TBI intake and heads. I can't remember the numbers on the heads but when looked up they are listed as heads that go on a crate engine. I bought it used with less than 5000 miles on the engine and it came out of a 1995 K2500. I don't mind changing the lifters and rocker arms and push rods along with the can if I can do so without pulling the heads off.