I believe you will need the Deviant action from Defiance for the .338 Lapua. You need to check with Defiance on this.
You need a .750 bolt, a receiver that can handle the chamber pressures and bolt thrust for this cartridge. The .338 Lapua is a different animal- and must be regarded as such.
I think you're making a mistake buying components- then trying to find a builder.
Interview gunsmiths, discuss pricing. Most of the time, you don't save $$ by buying your own parts, but of course you want to price both ways, or with a combination to get your best overall price.
It's kind of like buying your own starter at NAPA, then taking it to the mechanic to install. He might do it- but if that starter is bad out of the box, or fails under warranty, it's your problem. Most of the time, as FFL's we get pricing discounts so that we can make a few bucks- and still sell to the customer at the same street price he'd pay direct.
It'll probably take 4-6 months for the barrel anyway (if not the action as well), so take your time. However, if you're looking for something sooner rather than later the buying decisions/builder are going to be influenced by availability of components and the builder's backlog.
Personally, I don't want a $1,500 rifle that's running $4.00 ammo. I knew a custom build would be expensive going into this. I know you guys are trying to help, but this is not a "trying to save money" build. Not trying to be hostile, just trying to set things straight.
The .338 would be partially for targets but more so for hogs
There seems to be a "board mentality" where many here can't seem to comprehend custom builds- and why anyone would want to spend the dollars involved on one "When you can buy a Ruger American..." Suggest you take this to Sniper's Hide, and do a search there for information. We all know you can buy a single-shot Savage .338 LM for a grand- that's not what you're looking for.
You do have me really puzzled over the "more so for hogs", but what the heck... I suppose if you've got the open country there, and they're at 1300 yards it would be more interesting than banging steel.