c'mon you should have it perfect in a couple of days,btw there is a guy on the buy/sell forum that does photoshop artwork-maybe worth giving him a shout,might be able to recreate the original artwork.
the backglass is just a clear toughened glass over a plastic artwork sheet isn't it?
i think you got a pretty good deal,don't be too tough on the seller-very few machines of that age will be in perfect showroom condition,anyway half the fun is making it perfect yourself-you get a real "i did that" feeling,anyway good luck