A meter with a 600vac face might be way too large, i.e it might not be accurate enough if not digital.
The stability of digital reads can be fickle, can't be zeroed well, or are slow to showing change per build. You also want one minimum imo. Slow or sensitive, that fraction always works in your favor. 0-99.9v or even 0-99.5v in accurate half volts...would likely be fine. It's likely never going to 30v on a bad day.
120vac is way too much also. At 50v half of the meter would still never see use (until something was out of phase anyhow 
).
A 20-30v face would be great; note ZW 20v full throttle, so 25v ZW max with the +5v whistle boost. The 5v extra in fast accidents likely wouldn't kill a 20v meter, but hard to say when excess heat takes it toll ...it's just a tiny electric coil & a spring. (traditiinal analog anyhow..ie. how long at 25-27v? 0.2 sec. or 2 min ???)
