The modifications, to carry bombs under the wings, were “Special Order Only,” and could be fitted to either “E” or “C” wings; one was simply to fit deflectors over the ejector ports, so that empty cases did not hit the bombs, but the other appears to have needed a working party (at least,) possibly the attention of a repair facility, since it required work to be done in the cockpit. Under-fuselage bombs normally needed shortened vanes, to avoid contact with the ground. In all cases, the aircraft needed the four-spoke (i.e stronger) wheels.
The introduction of the “E” wing was held back until the arrival of the gyro gunsight, since the Air Ministry favoured the extra delivery, from the four .303″ guns (even though the bullets were lighter) rather than the slower-firing .5″, because it gave a better chance, in a deflection shot (at which a lot of the pilots were not very good,) of disabling the enemy pilot. With the new gunsight, there was a better chance of the pilot actually hitting what he was aiming at, so the .5″ came into service.
Years ago, a friend of mine found out that the .5″ was moved inboard, and forward, to make cocking them that much easier; apparently, in the outboard/aft position, armourers were ripping their hands on the aft part of the gunbay, and the cannon didn’t have the same problem.