Strange part # for my flywheel...

A couple months ago I added a SPEC billet steel flywheel, Stage 1 clutch, new trans etc. I pulled out the old flywheel weighed it 21 lbs. The spec weighed in around 26 lbs.
Now I checked the part number on the flywheel....no numbers match what I have. 10125380A then a space N Can anyone identify that part number?

Anyone have the GM number for the stock flywheel? Does anyone have a stock one laying around they can weigh to check the weight?