Chances are very good that the monitor is a standard res, unless the cabinet housed a game at some point that required a special monitor and the monitor was changed out. Never assume that the monitor is what was originally in the cab unless you know for sure because it could have been changed out at any time by an op due to failure or otherwise.
The first thing to do is identify the monitor by looking for a label on the chassis somewhere. Once you know what monitor you have, then you can search for a manual that will tell you where to connect the RGB, ground, and sync from the ArcadeVGA.