Got a fluidyne and a BlackMagic - love it. You can hear the fan running while you're sitting idling, I'm sure you can rig up an indicator light when the fan is on.
As far as the original question, I've seen info on the
www.flex-a-lite web site you can run upwards of 428,429s in Stangs - these are earlier mustangs. The best way to see if you can run your BlackMagic with your 331 is send an email to the following:
flex@flex-a-lite.com