Is it one of the old staggerfeed blind mag boxes?
If so I had one snap during removal and wound up shimming the bottom of the stock between the stock and the floorplate with some folded paper and the action screws hold everything in place. Not ideal but it works and feeds.
Sometimes ya do what you have to when dealing with old parts no longer in production and made of unobtainium.
Tried having the piece welded but it just snapped again.
Good luck.