Wayne;
Short answer, yes the 1917 action can be used for a 338 Lapua. I have 338-416 rifle now that is built around an Enfield action. I am building another rifle of the same caliber, but will be using a Nesika action. In my opinion, the Enfield is the premier older action to build a wildcat on, and is the strongest (debatable) military surplus action available. I love these old rifles - my first rifle was an NRA Eddybrook purchased for less than $20 when I was about 14 years old. I packed that unmodified rifle around the hills, using it for everything from hunting to plinking for over 20 years. Having said all that, I would not build another custom gun on the action. I paid $1,700 to have my action (a Remington) modified, including bolt work, bottom metal, ears milled off and rear of the action modified. I can buy the best modern action for that today, and the tolerances are a lot closer and the metal is much better quality. I feel a lot safer using the "new stuff." I don't regret the Enfield experience, and I will always have a soft spot in my heart for them, but for accuracy and cost efficiency, it's tough to beat whats offered now. Whatever you decide, have fun and good luck. If you go with the Enfield, find a smith that has worked with the actions in the past and knows what he is doing, the modifications are not childs play and I have seen some work that has reduced a magnificant old action into a piece of usightly junk.