Andy, the Spit is an airworthy MkV, clipped wing, which was flying for many years in the colours of a Czech RAF Sqn.
It's been under deep refurb for a year or two, and should be back in the air soon. During our visit last May, there were some (replica) Browning .303 MGs on a bench, which the engineers had made from scratch, presumably to fit to the wings !
It's possible that the cannon, and the ammo box in the background, were also built by the staff - wonderful work.