That scope is probably close to $1,000 all alone. Maybe a bit less. But nice ones with bases, etc. aren't cheap!
Whoever did the modifications to that rifle did a nice job. And you are right... a post-64 is not especially valuable. Until you get into things like factory target rifles.
I pulled this off another site and it is interesting because the post-64 target rifles may actually be better shooters than the pre-1964. Here is the text:
"...post 64 variations, such as the Ultra Match, and Palma Match rifles (1968,71 and 76). These were built in the custom shop with special attention given to their assembly including factory bedding of receivers with Bisonite, and externally adjustable triggers. Winchester took a great deal of pride in these rifles and they showed it, garnering praise from the International group of shooters that competed with them. All barrels were lead-lapped for precise tolerance and smooth finish. The latter targets used hammerforged barrels with extremely tight tolerance and concentricity. Winchester had never gone to this degree of attention and detail for any of their target rifles with the possible exception of the handful of single shot 70’s manufactured in the 1950’s, for the AMTU at Ft Benning for use in International competition. These are not even a fair comparison when you consider they were hand built exclusively under contract for the Army. I have test results from this group of rifles and they would not be anything enviable today. Even those, in my opinion pale in comparison to the quality and accuracy of the later rifles."
If you can figure out if yours is one of the Ultra Match or Palma rifles... then you may be looking at something really special.
If I were to pull a number out of thin air... I'd say if it really is a target rifle, even post-64, you would be looking at a minimum of $1,000 for the rifle. As much as the post '64's aren't collectible, try finding one for less than 700 - 800! And the modifications to yours look well done.
BTW, here is sort of a comparable. I'd not call this out of this world in terms of asking price....
https://www.gunbroker.com/item/1038009913
So I'd say you are looking at something that is probably well bought at $2,000. Probably REALLY well bought at less than that. And probably not out of the realm of possibility at $3k. Maybe more if it has a real history or if you can link it to the 'smith who built it. Competition guns are a thing.
Hope this helps! Big range, I know. And a lot of 'if's.' But unique things are hard to value, too! Maybe some of my fellow vintage fans will want to chime in and confirm or refute my thoughts!
Cheers,
Sirhr