Why not just modify MAME's crosshair images to a red dot and blue dot?
That was always my plan for IR guns on the LCD cab. (but I would go green dot

)
Never did check into what's involved.
On the digital leisure PC versions of the American Laser games, the crosshairs are an easily accessible PNG.
I made them blank for my Act Labs CRT guns.
With IR guns, a dot generated from the gun isn't going to be accurate anyway.
The angle and position of the gun effect the calibration.
What would be correct for you is going to be screwed up for someone shorter or standing in a different position.
Best to stay with the emulator created crosshairs as that is where the shot will go.