I will upload some pics this weekend. It's shell is pretty good only a few dings, but inside there is rust in quite a few scattered, but small spots. It definitely needs a sanding inside and out and a coat of paint.
Don't worry, if I were to mame it, I would not degrade the value of it by drilling new holes/etc... I would make board mounts (circuit boards like being mounted to non-conductive surfaces better anyway

) and adapt them to the existing mounting pieces, so it would be a cinch to convert back.
I got for a reasonably good deal (around $100), but I didn't know how different it was than from working with wood products and didn't consider a lot of the issues with that and it being nintendo and having 'special needs' compared to other games (e.g. 100 volt monitor, 110->100 volt power converter, negative video monitor, special nintendo joysticks, metal vs wood shell)
It has 3 pieces of graphics, all have been warped and need replacing. It had almost all the wiring (they chopped the wire right next to the power supply, otherwise all ends are there including the 2 prong AC line to the (missing) monitor. The vinyl fake red stained oak laminate is starting to peel in spots.
The joysticks were stripped out, the buttons were still there. The top glass has scratches and one edge ding (1/8") over player 1. The support legs are physically okay but look like he11--tons of grain-of-sand sized pitting on the pewter-like aluminum base (probably from aluminum eating floor cleaners) and no black (just rust starting) on the uprights that slide into the cabinet side posts.
It definitely needs work. I know I could sand it down, spray a new coat of paint, make some mounts, slap in an ATX power supply, ATX mobo, Duron 600 (O/c to 933) chip, 128 meg DDR memory, 4 meg AGP video card, 2.5 gig hard drive, a hacked Commodore 1084 monitor, AdvanceMame, and hack a single USB gravis gamepad to 2 replacement 8 way Nintendo joysticks I have for under $100 and have the thing playing every single vertical orientation 0 or 1 button game ever made, and no headaches with getting working classic parts.
I'd sand, reprime and repaint the top cream-white as it's got a fair amount of liquid damage (cleaner more than soda pop). I could easily iron on new real-oak laminiate trim and restain the deep red and it'd look even better than the vinyl laminite.
Just wouldn't be able to replace the slightly worn graphics around the P1 joystick.
I figure cost to mame: $0 == Nothing as I have all the parts ($100-$130 if I had to buy them all now), plus ~$20 in paint and laminate. (Value of selling parts , on ebay that I'd end up using are probably < $50 [half what it would cost for me to buy them there due to shipping])
Cost to restore to original DK: At least $300 all told. Need to get power ($50), monitor ($75), boards ($100), 2x 4 way sticks ($30), new graphics ($25 though I dont think the bigger instruction sheet for the cocktail was ever repro'd.. the smaller one on the uprights were), ~$20 paint and laminate. Don't think the thing would be worth $400 to resell though...
Again, I'll post pics this weekend, but I think my description above gives a good idea of where the thing is at...