Everything you have done with the carb you have is about right. Remember Doms. are made to be ran at WOT! Sounds like you need a smaller carb. I would try a smaller HP series carb, and see what it does for your application. Or try FI on this motor
Yes the dyno was done to find Max HP and torque for your motor. Not to make it idel without fouling the plugs. It's very hard to find a happy medium with a Dom at idel without fouling your plugs. What did this motor do on the dyno?