Or a playchoice 10?
I'm not an expert, but I think that the ol' crt tube's interfering with each other is a bit of an outdated notion. If your CRT's have degaussing coils, they should be protecting themselves from the limited magnetic interference of another CRT. I would think you could place a sheet a metal between the two to protect them further. Not to mention, I think that anything potentially damaging, you would visibly see color distortion when the monitor is on.