Jim, it's on the large starter housing driver's side, depending on the year they may be on the passenger side... stamped numbers...you really think you have the original starter in yours still?
I believe it is original. My Pontiac dealer repaired it 3/21/72 (63,664 miles) using new brushes, bushing, drive, washer, etc. The same dealer rebuilt it again 9/3/80 (150,358 miles) using more new brushes, bushing, drive, plate, solenoid, etc. Then in 10/13 (about 183,000 miles) I had it repaired at a local shop that sent it out to a rebuilder twice to get it right. So, unless someone did an unlikely switcheroo on me, it should be the original.