bobgifford,
Per " Hatcher's Notebook " on May 11 1918 the Rock Island Arsenal starting with reciever # 287,507 changed the heat treatment on all actions. On August 1. 1918 they started making actions of nickel steel with action # 319,921. Prior to 11 May 1918 actions were made of carbon manganese steel.
Due to several accidents which resulted in actions blowing up a special board convened. The board found that all actions made with the old heat treatment were to be recalled and destroyed.
The action on your rifle, according to this board, is unsafe to use. The book has several pictures showing actions that had blown up. I don't think its worth the risk of hurting yourself to use it. Sorry. I hope that this is of some help.