Master Model has a line of finely done brass parts which upgrade the kit they’re designed for. These parts are great if you have an accident and one of the cannons breaks off. The other possibility is AMS, as the machine guns are far superior in detail to the little nubs provided on the kit wing. See the parts comparison below.
The Spitfire IXe had a pair of 20mm cannons in the wing. These had been moved outboard to allow more ammunition for the Browning .50 caliber machine guns. The cannons stuck pretty far out from the wing, but the Brownings barely showed. The “fix” for the Brownings was to put the muzzle inside a tube which extended from the wing.
The kit contains six parts, two cannon barrels, two .50 muzzles and the wing tubes for the Brownings. The cannons for the early e wing were conical in shape. The later e wing had a more elliptical shape for the cannon fairings. This kit has the “late” cannons.