I too have a donkey kong cocktail but it's completly empty, and as the others have stated, it's not a great cocktail to work with because of the limited room. I'm planning on making mine a double donkey kong but i am going to make it jamma as trying to find the original parts for these nintendo cocktails like the power supply, sanyo 14" monitor w/ inversion board, cpo, & joysticks on ebay has not been going well at all. When a part does show up like the cocktail joysticks with the metal cpo, they go for over $100 just for that 1 part. So making it jamma (while not an easy feat in itself) makes it easier to get up and running. I still need to find a 13 or 14" monitor for my cab yet + the joysticks so i still have a long way to go.
As far as other jamma games, again you'll run into the problem of making it fit in the cab. The cocktail 4-board set is on a metal plate that slides into 2 vertical grooves in the cab. If you can get a jamma board to fit those same dimensions, then it shouldn't be a problem. Also, if your using the original sanyo monitor, you'll have to use that inverter from mikes to make the video display properly along with the sound amp.