That is a great idea for the LCD.

The GT cabs have that extreme angle for the monitor, which is good for the fingers and knuckles coming off the trackball, but probably not great for light gun action. I am humbled by your continued ingenuity on this project.
In regards to my earlier post, I figured that you could create a .reg file that the .bat file used by MameWah could load that might force a resolution change on your monitors.
i.e. - Launch Mamewah --> Mamewah runs .bat (batch) file --> .bat file runs .reg file --> .reg file forces your hkcc to change the resolution.
Since you got it to work without that, I'm assuming my solution was way more complicated than it needed to be. I haven't run Mamewah yet, so I'm not 100% familiar on how it works. Sometimes a fresh perspective helps, even if it's an idiotic solution like mine was. We always do that at work whenever there's a tough problem. Try and look from every angle, even if it doesn't make sense. It might lead to an epiphany, although more likely to a Miller Lite.