The contrary happened to me with an arcade monitor. It had only RGB input so, I couldn't connect for example a Spectrum(composite) to it. Also the phosphor of the CRT tube was wasted out, normal on that type of devices.
The solution?, I'm not an electronics expert as you, so I bought a second hand high line Sony Trinitron tv of the same proportions and shoved it into the arcade machine... It had the same diagonal inches, so it fitted perfectly the frame. Only the different curvature of the Trinitron tube didn't fully matched, but it looks acceptable for me now.
It has two Scart connectors, one for RGB, and now I can connect almost anything to it, with a remote control to easily swap video sources and tune the volume.
