Danny, just got off the phone talking to a lovely lady who is the museum director. The aircraft is definitely EZ999. The NH-Y markings are fictitious 12 squadron markings, as it was never issued to a squadron, in fact the aircraft never flew in Australia, the only hours being test flying it may have done after coming off the production line. Who applied the NH-Y markings is not known, nor the graphics on the nose. It spent all its life in Australia in crates. It did have a 50 cal mounted in the rear pit, but its not known when it was fitted, or by whom, now removed - didn't think to ask, but probably a result of the government gun buy back after the Port Arthur massacre.
The following links list the Vengeances built.
http://www.joebaugher.com/usaf_serials/1941_5.html
http://www.joebaugher.com/usaf_serials/1942_2.html
http://www.joebaugher.com/usaf_serials/1942_5.html
Dug out the history of the aircraft you mention that you flew
Danny. You got to have a story on 993 to tell.
Northrop A-31-NO Vengeance Vultee Model 72 built under licence by Northrop Ordered by the RAF as Vengeance I EZ800/818, Vengeance IA EZ819/999. Some were diverted to the USAAF and dispatched to Australia as part of a US commitment to equip the RAAF. None served with the USAAF. The balance were delivered to the RAF in India
EZ811 41-30859 to RAF as Vengeance I. SOC Aug 31, 1944
EZ834 41-30882 to RAF as Vengeance IA. Soc Apr 26, 1945
EZ86041-30908 to RAF as Vengeance IA. SOC Aug 31, 1944
EZ862 41-30910 to RAF as Vengeance IA. SOC Aug 31, 1944
EZ891 41-30939 to RAF as Vengeance 1A. SOC Aug 31, 1944
EZ894 41-30942 to RAF as Vengeance 1A. Crashed into Sea Dec 28, 1943
EZ904 41-30952 to RAF as Vengeance 1A. Wrecked when bomb fell off and exploded when landing at Kumbhirgram Dec 17, 1943
EZ993 41-31041 to RAF as Vengeance 1A. Crashed on emergency approach to Mambur airstrip, India Feb 24, 1944