[...Jane's Fighting Aircraft of WWII says the Mk XIV had, namely 2 20mm cannon and 4 .303 cal machine guns...Spitfire Mk XIVb]
This doesn't really have to do with answering your question, but is just for some reference. According to the Osprey Aircraft of the Aces Series (#5): Late Marque Spitfire Aces 1942-45 by Dr. Alfred Price, the Type C wing was called the "Universal Wing" because of its variable configurations. Armament-wise, there was provision for a maximum of 4 20mm cannon and 4 .303 cal. machine guns. In practice this max armament was never used (at least, I don't think so) due to the excessive weight of all the guns and ammunition. Armament combinations that were employed were 1) 8 .303 cal. mg's (rare) 2) 2 20mm cannon/4 .303 cal. mg's and 3) 4 20mm cannon. The most common armament combination for the Type C wing was the 2 20mm cannon/4 .303 cal. mg. A few Spitfires did mount 4 20mm cannon in their Type C wings, but it was rare due again, to the weight (the Spitfire Vc models delivered to Malta DID appear to routinely use the all-cannon armament, though, as availability permitted). Another interesting fact about the Type C wing was that it had interchangeable wingtips. You could use the "standard" tips, or remove them (and I would assume, add "caps") leaving the aircraft in "clipped wing" configuration, or substitute pointed wing tips (developed for high-altitude interceptors such as the Spitfire MkVII), which added, I believe, an extra 6 1/2 sq. feet of wing area. When the MkXIV entered service, it would have carried the "Universal" Type C wing, and most of these early MkXIV's seem to have carried the 2 cannon/4 mg armament. Later, the Spitfire MkXIV, and the Marks IX and XVI, carried the Type E wing, with 2 20mm cannon and 2 .50 cal. machine guns.
On the subject of the armament for these Spitfires, the book states this:
"Until the summer of 1944 fighter variants of the Spitfire were built with the 'C' Type wing, and the standard armament was two 20 mm Hispano cannon.....and four .303-inch machine guns.....
During a turning combat the value of the four Browning .303-in guns mounted in the outer wing was questionable. If the pilot was pulling 'G' when he fired, the flexing of the fighter's wings ensured that rounds set out in a quite different direction from where the gunsight was pointing. Another mitigating factor against the value of .303-in weapons at this stage of the war was that virtually all combat aircraft carried armour protection, which rifle-calibre rounds could not penetrate.
By 1944 the US factories were producing the Browning .5-in machine gun in such large numbers that the weapon was made available in quantity to the RAF. The Spitfire wing was redesigned to take the weapon, and the so-called 'E' Type wing had the cannon and machine guns re-positioned. The 20 mm cannon was moved from the inboard cannon positions to the outboard positions, about a foot further out. A .5-in machine gun, and a box with 250 rounds of ammunition, was installed in the space vacated by the cannon and its magazine. The .5-in weapons delivered a heavier penetrative punch than the smaller guns they replaced, and were far more effective for both air-to-air and air-to-ground fighting."