GM crate (old school) engine ?

[sactoC10]

OK, picked up the parts truck yesterday and originally I had no intention of keeping the engine or trans. Tow truck driver saw what was being moved and got all excited, telling me it was a factory crate rebuild in there...even offerring to sell/trade "whatever" for it.

Since we all know the saga of my mystery hose, I'm thinking that keeping this engine around is probably a good idea, but how might I identify it as any such thing? It is a 350 of course, and there was evidence in the glove box that it received a rebuilt engine as the yard manager stated.