Dive bombers had a "crutch" as mentioned above, that swung the centerline bomb down and away from the prop arc when released.
You can see the structure straddling the bomb in photos and virtually all dive-bombers had the device: Ju87, B5N, SBD, etc.
As for rockets, virtually all aircraft during the war, carried the rockets in "racks" beneath their wings.
The rack design ranged from tubes to wooden trays and were situated so they would not be near the prop arc, even on multi-engined aircraft. In the case of the rocket armed B-24, the launchers were mounted on the fuselage, below the cockpit and ahead of the main-wing.