Winchester never offered any detachable mount of their own, to my knowledge, and I think its absurd to say the G&H twin lever side mount reduces the value of a Model 70, especially since Winchester custom shop offered it. It is very functional, and adds a certain panache to a model 70. While the Super Grade stock was dressy for Winchester, it can't hold a candle to the G&H stocked guns.
I wish I still had the G&H built 7mm Mauser built on the '03 receiver. The John Warren engraving of bolt cocking piece, receiver ring tops and muzzle were the frosting on the cake, But I suppose the diehard Model 70 people would have found something to pick on.

I don't think the G&H side mount devalues any gun. I've got a bag of rifles with this mount and don't really care whether G&H installed them or not if it is a clean installation.

I totally agree. I really like the G&H side mounts with vintage era scopes. The setup allows easy loading, ejection, as well as the unobstructed use of the peep sight.
Edgar I wish I could have handled your G&H rifle.
This rifle has some really nice wood but I agree G&H stocks were exceptional.