I have successfully used a brightness/contrast PCB from a Macintosh Color Display to run a CC as an external monitor, with no monitor attached. Voltage-wise it doesn't give the full range that the CC uses, but it's useable. Brightness goes from totally dark to useable (but not really bright), but the contrast changes only slightly. I used 5v for the input from the ADB power pin. I post this as a useable solution, but ideally one might be better off building one from scratch.
On a less happy note, I have been unable to get a 575 a/b to work the same way as a CC board. The CC board crackles up and displays when it receives a proper sync signal; the 575 board does not, as far as I can tell (it emits a sound as it powers up to stand-by, but never gives the loud crackle associated with getting an actual picture). I have only been able to get the 575 a/b to display with a 575 m/b attached to the harness.
I'm disappointed because I had been intending to use the 575 board, as it gives SVGA nicely with the stock CC yoke; I got it to display SVGA with good geometry and only 1 cm black borders, and with none of the convergence issues associated with the 575 yoke. But it doesn't want to sync and power up (and yes, I tried putting a load on the fan, grounding ADB, etc.) with an external video source (needed for my particular project ;)). Perhaps I'll just make do with VGA
And, on a happy note, the CC FAQ is back! Thanks Chris.