Gibson serial numbers were for a long time not very reliable. Epiphone became the budget label for Gibson at some point within a few years of 1959 (not sure exactly when; somebody else will know) and some of their guitars were very nice, but for some reason I doubt this one is as old as they are telling you, and, unless this is a really special individual guitar, you can do a lot better than that for $850. Try checking the dealers given above and maybe the auctions.

Chet W.