The only question with the defensive guns that is still wide open is the lead computing computers the B-29 had, will this be a feature defensive gunners will have at their disposal while gunning in a B-29 in AH? Nobody (unless you live or work at a certain company in Grapevine, Texas) knows yet.
It is presumed that the defensive gunnery will be the same as it is in every other defensive gunned plane in AH, positions # 2-X for the various gunner/observation points located throughout the plane, you point with your crosshairs and shoot with all defensive guns that are capable of shooting in that direction being linked together to shoot where you tell them to in relation to the position you're manning at a convergence of ~500 meters.
We currently have multiple bomb bay bombers in the game, all bomb bay doors are controlled together and in unison as if they were one single bomb bay.