McMillan A-4 Stock barrel fit?

Build an AR-15 first. You only need a couple of hundred dollars worth of special tools to do that. There is no fitting or machining required for the AR-15. It is just a slap together fit. You are talking thousands of dollars of tools to build a custom bolt action rifle. If you want a good custom bolt action rifle, find a maker that makes ones similar to what you want, tell him specifically things like weight, accuracy, size, caliber, and stock material and let him work out the details like barrel and such. P.S. If you need someone to drill the stock, you have no business trying to build a rifle. P.P.S. A Rem 700 receiver and bolt will cost you more than a Rem 700 rifle.