It's difficult to track down such information, without having access to Log Book details, or perhaps a photo showing his use of a specific aircraft, more so with the Mitchell in RAF service in general, and the MkIII in particular.
I've been studying Mitchell squadrons, and planning to do a 1/48th scale MkIII, and have probably seen most published photos, plus some I got from the Imperial War Museum for an article 25 years ago.
The most numerous type was the MkII, in two versions, (B-25C and B-25D), and by the time the MkIII came in to squadron service, the Mitchell squadrons had moved to the Continent, in September 1944, and were based mainly at Melsbroek, near Brussels, with a mix of Mitchell MkII and MkIII aircraft.
The MkIII tended to be somewhat cleaner in appearance, compared to the earlier ones which had seen much service, and were delivered without 'Invasion' stripes, which were not applied in the field either, as it was thought not worth the effort, with camouflage being the standard Olive Drab (or equivalent colour Dark Green, a paint close to OD) over Neutral Gray, with Dull Red codes, those for 226 Sqn being MQ, and the individual letter was carried on the nose.
An example of a Mitchell III from the Squadron is serial number KJ561, codes MQ-Y
Not much, but hope it helps.
EDIT: Forgot to add - contrary to common belief, a crew did not always use the same aircraft all of the time, although 'senior' crews, particularly higher-ranking members such as Flight Commanders or Squadron COs, tended to do so. A crew might fly the same aircraft on a number of Ops,and might have a preference for, and try to 'stick' with a particular one, but generally, it would be the aircraft assigned for a particular operation.