Check this out:
http://www.gibson.com/Whatsnew/pressrel ... an29b.html
Given that the Beatles all got Epiphone Casinos in the mid '60s (McCartney in 1964, Lennon and Harrison in '66) and used them extensively, I'd say a mid-'60s Casino would be considered a valuable guitar. If it were mine I'd probably pick up some decent chrome dog-eared P-90s for it. I don't think I'd bother looking for original '60s Epiphone pups or other old parts. I might not bother with the pickguard. AFAIK, once Lennon had the finish taken off his Casino he didn't put the pickguard back on. See pictures of the roof top concert.
Bottom line, I'd keep the guitar and love it and play it, but I wouldn't be too concerned with putting back to original except where there's a functional reason to do so (e.g., putting a pickguard on because you prefer having pickguards). That's me though. Congrats on your find. :)
-Scott