Well, you've heard from the "purist" camp, the rifle is "ruined" and not worth it (whatever price "it" turns out to be".
On the other hand, someone turned what was, I'm sure,
at the time, an ordinary plain jane pest rifle into something that both fit and shot better.
If you are still inclined to buy, start with asking price, subtract cost of getting another stock (original, maybe Numrich Arms), plus removal of scope, filling & refinishing of tapped holes, gets you down to legitimate offering price.
That would be one way to go about it. However, "legitimate" can differ in the eyes of the bidder and the seller.
Personally, I would be a bit insulted if it were my gun, and you took that route. An offer less than what is current market rate for an unaltered collectible original? I would accept that without insult.
But an offer expecting me, the seller, to PAY for the work YOU want done (by reducing my asking price) is insulting, to me. Simply put, if you want, and will only be happy with an original condition collector's piece, go buy one.
Turn the idea around a bit, say I have a stock Colt Govt Model for sale, and you want a gun with all the "bells and whistles" found in competition guns, would you expect me to lower the asking price to compensate for the cost of the extras you want to add? I don't.
Its a "period" gun, with period optics, added in a day when a scope was a rare and uncommon thing. Personally, the only "ugly" thing I find about it is the stock carving is not to my taste. If it had been finely checkered, or even basketweave, it would LOOK better to me, but that's only looks.
If you want a period original piece, buy one. If you'r going to buy a "period custom" piece, don't expect the seller to pay for your cost to restore it to period original condition.