I would call Barry Grant and ask them what carburetor they recommend for the application. I know that they make Demon's specifically tuned for certain crate motors like the ZZ4. So they might have one that's already tuned for your motor.
By the way, I'm running a 750 speed demon on my 383 in my Elcamino, but when I went to a higher duration cam we actually had to modify the carb to basically what a Mighty Demon is out of the box. So as I stated above, call Barry Grant for your application.
Basically a Road Demon is for a lightly modified engine.
A speed Demon is good for up to about 236 duration @ 0.50.
A Mighty Demon picks up where the Speed Demon leaves off. And then there are the race Demons
The only complaints that I've heard about Demon carbs are from people that didn't research the carb that they bought to make sure that it would work for their application.