Kinda funny you asked that ...

I'm actually working with a Galaxian cab right now. I have an empty 25" monitor frame that I had placed in there just for fun to see how it would look, or work ...
Kepp in mind, this could probably be accomplished, but not without making some serious mods to the cab ... mostly for reinforcement. It was really cramped though ... too cramped if you ask me.
For a midway cab such as that, I think I'd stick with a 19". Just my opinion though...

FWIW ... the specs I have are W-23"/D-21" ... if I took those correctly. The D of course being the monitor mounts that are already inside the cab, depth-wise.
Hope that helps a little.
Michael