Hi I would remove the recoil plate & look for a third hole in the middle of the wood . Indicating a standard m2 stock miilled to fit the wire stock recoil plate . There should only be 2 holes As for the 7/4 rivets .I believe the 7/4 is simply the size . ie # 7 being the dia and 4 the length . Most rivets are sold in 1/16 lengths as I recall so 4 would be 1/4 .Yes those rivets were used back in the day before brake shoe lining were bonded .I have used the 7/4 rivet to replace worn leather many time in the past , A simple aircraft hand riveter will roll the rivet nicely .

Hand Rivet Squeezer Aircraft Aviation Tools | eBay