If you are after a primer on RAF Allison engined Mustangs, this recent thread over at Britmodeller has some good reference material and information.
A Few Mustang Mk.i Questions - Britmodeller.com
Also the following might be of interest.
RAF Allison-Powered Mustangs - Cybermodeler Online
The armament on the three Allison engined marks of Mustangs used by the RAF were not interchangeable. The aircraft were fitted with one type of armament fit that was not interchangeable between marks. The wing designs and armament mounts precluded any swapping, similarly the nose mounted MGs of the Mk.I could not be fitted into the Mk.IA or Mk.II as ancillary equipment was fitted into the space left by the removal of the MGs on those marks.
For the Mk.I, normal camera when fitted was a single F.24 oblique fitted immediately behind the pilot's head in the cockpit. A limited number of Mk.Is had a vertical camera fitted in the rear fuselage between the radiator outlet and the tail wheel. For the MkIA, again the oblique camera behind the cockpit and a greater percentage with the vertical camera. For the Mk.II a few more camera installations were developed and used. But basically the Mk.II had the oblique mount as standard and by late 1944 the majority had the vertical mount as well. A number were modified to carry a dual oblique mount, with two F.24 cameras immediately behind the cockpit - it was a tight fit. A very limited number, a handful of Mk.IIs were especially fitted with a five camera rig - the two obliques behind the cockpit, a further two obliques mounted in the rear fuselage (not the same as the set up on the Mk.IIIs, but higher in the rear fuselage) and one vertical , in early 1945. The Tac/R Mustangs, which is what they were primarily used for, were not fitted with underwing stores carriers - the Mk.IIs had the wing mounting point but the RAF did not fit and use the stores carrier on theirs.
The photo of Mustang Mk.II FR900 M is scanned from Volume 4 of 2TAF by Shores and Thomas. The photo was reproduced in 2TAF with my permission as were a number of my other original photos in other volumes of that series.
Also AM and Hobbycraft, despite being provided with correct information before their releases, got the details of their subject aircraft wrong as shown on their instructions and box art. Mustang Mk.IA FD472 'M' was serving with No.268 Squadron, not No.168 Squadron in 1944 - something originally published back in the 1970s and perpetuated since. Also the subject aircraft with the Malcolm Hood and coded FD465 'N' is not listed as having served operationally with any RAF unit - likely again a continuation of an old piece of incorrect research, misreading the serial on a photo or similar.
A word of caution, the camera and mount pictured a few pages back in this thread is a representation of the USAAF type mount, not the RAF one, and a rather inaccurate museum representation at that. If you go onto the Imperial War Museum website, into their photo collections search and search under "Mustang" it will bring up a number of photos of RAF Allison Mustangs, and also the RAF style cameras and mounts.
HTH
Regards,