The pistons for 383s are typically short. Or, more precisely, the blocks are tall. So you will want to budget for, and make sure that the shop does it and sets them to zero. I agree on not running the MP stuff, and I personally would keep the Edelbrock carb if its a street car first. All carbs will need some tuning and setup to be right, but against each other, most carbs are very close to each other power wise. Carter/Edelbrocks will idle better and get better milage on the whole. I built a similar combo some years ago. KB flat top hypers, 906 heads, and ran the XE268 Comp. It makes about 400hp, 450 torque, and pulls past 6K, idling at 650 rpm. Nice combo, really.