Joe, it's a complete shot in the dark. Those numbers always pretty much come up with the tranny combo. Everything else gets listed on the build sheets to tell the line which part to put on, what tells them about driveshaft. Box 19 on the build sheet lists the drive shaft code I believe. BY on the M21 cars and BA on the M40 cars. The GM of Canada code has something to do with tranny's or related parts. Comes from the GM microfilm that tells what parts came on the car. Like I said, just a shot in the dark, if nothing else it makes for good entertainment for the night.
Peter