It's pretty unlikely you'll be able to get a twin carb rig to idle slower without creating a bog when you try to take off from a stop. You can completely ignore the factory specs on that rig- - - - -way too many modifications. Just shoot for a smooth takeoff without Dieseling on shutdown. Camshaft profile and manifold vacuum will make a huge difference on idle speed, also.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!