I can not recommend a smith in your part of the woods. But can attest to what a great rifle you are wanting to build. I did one myself. I used a stainless Mark V action and a 28" Lilja barrel with a 1 in 10 twist chambered in .338 Lapua. It was and still is a great rifle with many kills over 1000 yards, all one shot from a cold bore with either the 300 SMK or the 300 Berger OTM. Having owned many 378 Wby rifles I totally under stand why you choose Lapua brass. When loaded to max the Wby, Norma brass will have loose primer pockets in 2 or 3 firings. The 338 LM brass however went 15 firings with full house loads.
If I were to build this rifle again the only changes I would make would be to go with a 30 or 32" barrel and also I would look strongly at doing a 338 Lapua AI. The added velocity coupled with high BC Berger makes the wind drift much more manageable.
Here is a pic of the rifle we dubbed " Ole No Sneak"