It wouldn't really have been possible. Quoted rates of fire were averages; different guns would fire at different rates, the same guns would fire at different rates as they aged and loosened up; different ammo batches might affect the RoF, the temperature would as well, and so on.
The only examples I know of where it was important to fire the guns simultaneously (or as near as makes no difference) concerned aircraft like the Hurricane IID with two underwing 40mm cannon. Otherwise the unbalanced recoil would cause the plane to slew off-target.
Tony Williams: Military gun and ammunition website and discussion forum