We know the Hurricane has four size 3 guns on the turret. Will it be able to remove the four size 3s and hook up maybe two size 5s?

No. The turret is just the four size 3 guns. Now, on the infinite timeline, if we ever offer any swaps for the manned turret housing, who knows, but in terms of what mounts the ship has, it is four fully separate size 3 mounts on that turret, so you wouldn't be changing any of the sizes for it.