I am just a newbie, but many smiths warned me against the 700 action for the 338 Lapua. I cant remember the exact reasons, but it may have been also for the fact that the 338 edge was an easier option for like performance with less fuss ??
There are some real experts that will jump in and put you in the right direction. I have a couple of friends who built Lapuas on Nesika and Lawton actions.
Just trying to be of assistance.
With each step in the bush, you are a step closer.