The lack of the spacer, if indeed it was NOT there when bedded, would have allowed the action to be warped, therefore the bedding is warped. Your rifle is not going to shoot like that. Trust me...been there done that. You should be able to get one from Brownells etc. The spacer also acts as a trueing device for the action, in if the rear guard screw contacts the spacer and is hard to screw into the rear of the action, the action is not square to the bottom floor plate.
If you really look at Mausers design, with the rear spacer in, you will realize it is one of the first, if not the first, to be piller bedded. Another reason the stocks of mil.spec k98 are so well machined, and the recoil lug engages the steel insert in the stock. Get a solid square foundation for the action, and the gun will shoot.
Good Luck
