I'd say it's not worth restoring back to DK or whatever it was unless you are a big DK fan. Generally if you need Nintendo parts I'd check Mikesarcade.com since he specializes in Nintendo games. You can at least price out what you'd need that way. I'm not a huge fan of 60-in-1 boards, but if you can get SF2 running then it's already wired for JAMMA. Would be a simple swap with a 60-in-1 to get it going.
For me I'd want to ID what the cab was. I'm obsessive like that. Any chance the Nintendo serial number plate is on the top-middle on the back? I'd also loosen the coin door frame to see if you can see a color underneath. Might also be unpainted under the SF2 overlay on the front. Barring that I'd try CitriStrip or SafeStrip on a bottom-back corner where it'd be less noticeable.
Here's a list/picture of every Nintendo cabinet. Odds are it's DK, Popeye, or DK Junior:
http://www.ukvac.com/forum/nintendo-video-arcade-machine-reference-19781985_topic352997.htmlIs the speaker still behind the logo overlay on the front? That would have to sound horrible.
STANDARD CAVEAT: ELECTRICITY CAN KILL YOU. DON'T GO POKING AROUND IF YOU DON"T KNOW WHAT YOU'RE DOING AND YOU'RE NOT PREPARED TO BE CAREFUL. IF YOU"RE CHANGING FUSES OR MESSING WITH THE POWER WIRING UNPLUG IT FIRST.
In most cases if I'm getting nothing out of an old conversion, there's a few steps to figure out where power is going wrong. If it's plugged in and you flip the switch, are you hearing the monitor get voltage? are you seeing the monitor's neck glow orange?
ON A NINTENDO CAB, DO NOT PLUG THE MONITOR IN AN EXTENSION CORD TO TEST IT! The Sanyo 20EZ in most Nintendo cabinets runs off 100v (less than your standard US 110v outlet) which is why it's plugged into that outlet in the bottom.
If you see/hear absolutely nothing from the monitor, check that the volume adjustment on the SFII board is not turned totally counter-clockwise You usually don't have to turn it much to get a suitable volume. if you crank it these games can get LOUD. Try adding coins and see if the game will play "blind". Adding multiple coins should make a sound if the board's working (and sound works on it). If you still are getting nothing at all I'd unplug it and check all the fuses before breaking out a multimeter (If you don't have one, you'll need it eventually). Could also be an issue with the power wiring in general or a bad switch.
If the monitor is coming on but the game seems unresponsive, I'd suspect a bad power supply first. You can check the 5v at the power supply terminals with a multimeter to see what the voltage actually is or just spend the $20-$30 to replace it.
EDITED TO MAKE THE ADDING COINS COMMENT CLEARER