I have a Pre-64 (1952) M70 .375 H&H in excellent original condition (pretty much new) that is appraised at $4200.00 to $4600.00 but it's not a custom piece such as the one you're looking at. I would think that if the engraving, inlay, and custom stock was done at Winchester it would be worth quite a bit more. See if there is a Winchester collector's forum on the net where someone with a more in-depth knowledge of these things can help you.