try this for your idling issue. what is the new motor with cam and etc? how much different is it vs a stock 350 vs your 383?
take a combination of the two and use that for your idle and part throttle fueling. a Boosted tune isnt that much different then a NA tune untill you see over 105 kpa. Since a NA motor is 0 to 105kpa your tune in that sector shouldnt be much crazier then it would be if the turbos arent on there. once you see over 105kpa then that is when you need to start really playing with timing and fuel
one thing youll have to tune around is that style intake your not running. that will take some playing around with since the air coming into the motor isnt how your used to tuning with.