If you want to stick with your current plastic bottom (Axis style) clip, then you just need to order the plastic DBM frame that holds the clip in place. I would also order a metal trigger guard with front bolt release cut-out. You will only be able to order the plastic frame direct from Savage Arms Parts. I have never seen the plastic frame stocked by any site vendor.

If you want metal, call Jim at Northland Shooters Supply and tell him you need the metal frame and bottom cap for a Savage SA or LA centerfeed DBM stock. You do not need another magazine box and follower. Just squeeze the sides of your current DBM/clip and pop off the plastic bottom cap. Replace it with the metal bottom cap.