All that needs doing is change the .50 cal to .303 on the XVI.
And the engine down rated.
http://ram-home.com/ram-old/spitfire-9.htmlWith the arrival of the Fw 190A on the Channel coast late in 1941 the RAF faced a serious dilemma. The new German fighter outclassed the Spitfire Mk.V on nearly every count, so the need for an improved Spitfire variant became paramount. But it was also felt that the introduction of a radically changed development would take too long and seriously interrupt production and operations at a critical stage of the war. So an interim solution had to be chosen, which was basically a more powerful Mk.V and could be produced and delivered to the squadrons with the least possible delay.
This interim type was designated Spitfire Mk.IX and consisted of a basic Mk.V airframe married to a two-speed two-stage supercharged Merlin 61 engine rated at 1,565hp which drove a four-blade Rotol propeller. Apart from the changes necessary to install this engine no other changes were made to the basic Spitfire V airframe. Externally the Spitfire IX could be distinguished from its predecessor by its four-blade propeller, the six individual exhaust stubs on each side, the symmetrical radiators under the wings and (late aircraft only) the enlarged vertical fin. These differences normally could not be recognized at combat range which provided Spitfire IX pilots with some tactical advantage at first, when their machines were mistaken for the inferior Spitfire Vs by their adversaries. The Mk.IX entered service with the RAF in July 1942. Later in its service life this variant was employed primarily as a fighter-bomber, having been replaced as an interceptor by Spitfire models with Rolls-Royce Griffon engines.
Depending on the particular version of the Merlin fitted, the Spitfire IX was built in three sub-types:
L.F.Mk.IX, a low-altitude fighter with 1,580hp Merlin 66 (4,010 built) F.Mk.IX, a medium-altitude fighter with 1,565hp Merlin 61 or 1,650hp Merlin 63 (1,255 built)
H.F.Mk.IX, a high-altitude fighter with 1,475hp Merlin 70 (400 built)
The L.F.s frequently had clipped wings, which improved performance at low altitudes, but apart from this feature the three sub-types were externally indistinguishable.
As with the Spitfire V the wing/armament layout was denoted by a suffix letter to the designation. Besides the "B" (only on a few early machines) and "C" wings already used on the Mk.V the Spitfire IX introduced the so-called "E" wing. This wing had the two 7.7mm machine guns replaced by a single 12.7mm Browning gun. This gun was installed in what had been the inner cannon bay of the "C" wing and the 20mm cannon was moved to the outboard position. So the total of 5,665 Spitfire IXs delivered consisted of the following sub-types (source: Profile Publications, No.206):
L.F.Mk.IXB, L.F.Mk.IXC, L.F.Mk.IXE
F.Mk.IXB, F.Mk.IXC, F.Mk.IXE
H.F.Mk.IXC, H.F.Mk.IXE
In later years some Spitfire IXs depending on their role received the designations F.B.Mk.IX (fighter-bomber), F.R.Mk.IX (fighter-reconnaissance), T.T.Mk.IX (target towing) or MET.Mk.IX (meteorological). A further development of the Spitfire IX and the last major production variant (1,054 built from 1944 onwards) with Merlin engine was the
Spitfire L.F.Mk.XVIC or E (with a Packard-built Merlin 266 of 1,705hp), a fighter-bomber which in its later versions had a cut-down rear fuselage and an all-round-vision cockpit canopy (one source quotes that this modification was made on some late Spitfire IXs also).
