OK, sorted it out. I hooked the monitor up to the IIsi, and it's running with a screensaver.

I originally had it plugged into the 475-for-spares. However, that's got something of an identity crisis going on. I put on the cover I kept back from the LC I had to throw out a while back, but the anti-static cover from the 475 is designed to have that trademark Apple SuperDrive disk doo. That means I can't stick floppies inside it, because they end up hitting the metal!!