Look on eBay. There are often pre 64 stocks. I have seen some nice ones for $250ish. It will be cheaper than custom. Harrod and others make wood replacement stock.  

You might find a local gunsmith with a Hawkeye Borescope to look inside those barrels to access wear. 

First to note, considering a Forum of collectors here. I do agree that many fine old “pre ’64 Model 70 rifles, languishing between not capable/worthy of restoration and not exactly either ‘pretty’ or field-functional in contemporary sense. On that basis, I believe your inquiry legitimate here and that these genre rifles particularly worthy of custom guns where converging stars of ‘condition & chambering’ make it so. That said…

Plans really depend so much on where you are – beginning with the rifle and where you intend to go with it. And also, if as most of us, very much upon budget. First you refer to blueprinting the action. Why; what to be achieved? Target rifles, perhaps. CRF field rifle – other animal to my mind. Particularly in the quality of the pre ’64 Model 70. Such for what it already is and its intended function. I don’t see what to be achieved in terms of returns.

Bore condition perhaps quite predictive of barrel ultimate fate. IF mediocre, I’d not mess with it. Simply to replace and there too, opportunity to express your own tastes. Again, if me, I’d probably just seek a pedestrian exact Win replacement in nice shape, reblued within spectrum. (*See a reference below.) The rifle you’re acquiring, if original, I believe should have an integral front sight ramp. I very much admire this feature. A trimming of length would remove that, but the 26″ barrel length was purpose-designed and suggesting you keep it. The action itself, as a factory product, is about CRF perfection to my humble opinion. A blend of best quality obtainable at a standard manufacture price point, as particularly, labor costs still comparatively low. We today, are the beneficiaries of all this and a rifle which would cost a tidy sum were it being now manufactured in the true pre ’64 mold. Just the 4140 Chrome Moly steel employed in the several principal components, seldom to be found in any mass production rifle nowadays.

A restock could be about as pricey as to imagine. But a quite decent gun for taking into the field; from what you say, I envision a basic form akin to the Super Grade lines. Quite possibly an acceptable stock to your liking is even yet lurking within the existing stock. I don’t know and getting beyond my comfort zone, only to suggest as possibility.

One of my absolute nicest stocks factory and surprisingly on a 458 Winchester chambered Zastava Whitworth mauser set up as classic “Express Rifle”, right down to the “dress parade”, multi-leaf express sights! Figured walnut in absolute classic lines right down to shadowed cheek-rest. Not a huge Zastava fan and no intention to buy until unexpectedly finding several to my liking! The quite decent, classic stocks on each that sold me. Pix below.

Sights. Just to mention, though not particularly popular nowadays and especially within precepts of such as 300 H&H, I like such as Lyman 48 receiver sight. One on my .338, vintage 1960, pix below too. Super Grade stock (perhaps custom shop rifle). Especially if your action is not receiver bridge tapped, perhaps to leave it so unless you deem “scope necessary.”

Sounds like an exciting project. A have several 300 H&H Model 70s. One prewar & two fifties era. None outstanding, but I enjoy them. The notation that such chambering with classic gentle sloped cartridge shoulder an ‘easy feeder’ and to my mind, slightly more reliable.

Well, now just to begin my descent… from the soap box!
Best of luck to you. I’d like to hear how it all turns out!
John

(* https://pre64win.com/ A shop which offers components and potentially useful if only as baseline reference. No personal reference one way or another.)