Rebuilding the engine and have a part that I don't know where it came from

that looks like a restrictor from the power steering line on the side of the rack & pinion.

Did you have anything other than engine rebuild work done? Does the hole go all the way through? If it does see if there is enough oil left inside of it to determine what kind. You can check for color of fluid and for what type of odor the fluid has.

try taking the part to a GM dealer parts dept they can tell you exactly where it goes. it is deffinitely for the oil flow the only other place i would say is the oil filter housing.

Did you have any luck finding the location of this piece, I have the same part left over after a rebuild on a 2.2 sunfire. I took it to the dealer and we couldn't locate it on their breakdown. I have low oil pressure at idle and I'm thinking it belongs somewhere inside the engine oil galley's, but haven't had any luck as to location yet. It does appear to be a restrictor of some sort though.