well......DUUH! I have all these books and I never thought to look at them!
About 5 seconds after opening Vol. 1 I was reading all about those buttplates. I had called mine a Schuetzen but they were known back in the day as Ballard buttplates. Evidently Winchester got them from the same supplier as they are a direct replacement. A bit later, they designed their own with the top tang to match the inletting of the regular butt plates. They did offer a Schuetzen model (mine was a Special) and that had all kinds of options...including a palm rest.