Is this true? Native resolution 512x480 @ 30Hz for those games. What kind of monitor can do that? GM creates interlaced modes and it doesn't look too good. What would you suggest?
Some Bally Midway games originally used interlaced modes to allow high resolution sprites over low resolution backgrounds. An interlaced mode of 60 Hz only updates a full frame only at a 30 Hz rate, that's why MAME reports that speed and it's perfectly correct.
As a fact GM (just because it can!) renders these game as progressive when you use a 31 KHz capable monitor, but this is plain wrong in terms of accuracy.