My 38 (early no series) also has the solid stock ,but my 38 was sent to a school, so it has the rings around the mum. Someone on the surplusrifle forum said that they might have been rebuilt before being sent to the school and a later one peice stock was put on it.
I went back to the thread I mention on the other site and the moderators stated that kokura arsenal used soilid stock's on some of their rifle's.
Hope that helps
Phil