I just did a 300 RUM build off a 700 action.
PTG one piece .704 bolt
PTG Saco extractor kit
PTG speed lock firng pin assembly
PTG HD recoil lug
40 MOA NF rail
Ultra light NF rings
27" Broughton 5C Med Varmint Sporter Contour - no flutes
SSG muzzle brake
HS Sendero stock skim bedded
Smith put in a center feed WBY mag box with 3.82 inside dimension. It will barely work for my throat and loads but if I had to do it again I would go with the Wyatts extended center feed which has 3.99" inside dimension.
So you might consider an oversized (.704) one piece bolt and sell the donor factory bolt.
And you might also consider the mini M16 extractor or Saco extractor kit.
Definitely get the extended center feed mag box and follower.
I might also consider a heavier contour with a 29" barrel, especially if fluted.
Other than that it looks good to me