Speed Demon should be more than adequate I believe. I ran one on my 408 with Twisted wedge heads...almost 11/1 compression and a Weiand Stealth manifold. It performed well. No problems with gas as long as the engine is built with a zero deck height and all the combustion is in the head and not down in the cylinder...no pinging whatsoever ( although this has nothing to do with the carb ). The only problem I had with the Demon was hard stopping....it tended to flood out and wanted to stall no matter how I adjusted the floats. I also had problems with the float bowl screws stripping out. The aluminum body on a Demon is much softer than the
zinc on Holleys and the early Demons had 12-20 screws that barely grabbed with 4 threads when fully tightened.....Newer units have about 8 more threads on the screws...still not great, but better.
I ended up changing back to an Edelbrock (AFB) 750 and basic as it is I love it...it never screws up and by the feel of it makes as much power as any other carb I've run.. ( next try is a Holley 950 Commander fuel injection that's sitting here... I hear the throttle response on them is great..)
