No purchase necessary.

Remove the bottom part of the box magazine by squeezing the sides of the box near the bottom and wiggle off. Now all you need to do is insert the bottomless box and spring and follower into the stock's mag well.

COrrection: you will need a metal "L" clip to hold it in place. the clip wedges between the rear of the mag and the rear of the well, with a lip hanging up and over towards the rear action screw. PM me with your address and I will send you one for a few bucks or call savage customer service, parts dept.