Tweety1
This is what I found in relation to the CAC Mustangs:
The 200 Australian built Mustang's comprised 80x CA-17 {Mk-20}[A68-1 to 80], these were built up from sets of imported components.
28x CA-18 {Mk-22}[A68-81 to 94 and 187 to 200]: 26x CA-18 {Mk-21}[A68-95 to 120]: 66x CA-18 {Mk 23}[A68-121 to 186]. All were based on the P-51d, with some minor modifications, the Mk 22 was a Tactical Reconn version, with two camera's in the rear fuselage, the Mk 23's featured the Rolls Royce rather than the Packard version of the Merlin engine.
All of the CAC Mustangs had the Dallas Hood, all had shrouded exhausts, internal and external apearences was not changed. Both the Tamiya and Hasegawa 48 kits give you a choice of hoods.
I hope this helps
Rob.