Ron,
As I don't want to infringe any copyright on Mr. Shattucks page, I'll just point towards a picture on his site:
http://gmund.rennlist.com/luger/tn_21.jpg
This shows the stock-lug attachment on the grip, which shows signs of being screwed, rather than being pinned. Note the small indentations on the sides of the round 'attaching device'. The stock itself will indeed be dovetailed into the stock-lug attachment, but the attachment itself can be screwed onto the grip and I think it is in this case.