Welcome to the site. Congrats on the new buy.

- You will also need a new magbox and follower unless you plan to shoot it as a single shot. Then you just need a single shot follower.

- If your Stevens is brand new it is most likely a centerfeed mag system, so a Boyds stock will have to be modified a tad to fit it. Theres a notch at the rear pillar for a bracket to fit in that holds the magbox in place. The other thing the stock could need is the magbox set in at the right height since it mounts into the stock.
*FYI, check with Stocky's gunstocks as they sell stocks just like a Boyds and also make them for centerfeed systems.
-When you change the bolthead be sure to check the firing pin protrusion. The mag bolthead may be thicker.