Australia operated aircraft EZ880 to EZ888, EZ905 to EZ915, EZ918 to EZ929, EZ930 to EZ974, EZ995 to EZ999 inclusive. All those serials were Mk. 1a. the RAAF also had Mk. 2a, Mk. 4 and Mk.4a.
EZ999 history is listed as,
RAAF Serial A27-99, USAF Serial 41-31051, Type A-31-NO, Line Number 320, Version Mk.1a, Contract RFDA-2648, Serial Number 720
Rec 2AD ex USA 20/06/43.
Rec 2AD 30/10/44.
Issued 2CRD ex 2AD for storage 12/02/46.
Authorised for write off 16/05/46.
Rec 2AD ex 2CRD 05/06/46.
Approval to transfer to RANFAA for ground instruction 27/04/48. Cancelled 11/06/48.
Passed to DAP 24/06/48. Issued to DAP 17/09/48. SOC 06/09/49.
Was located at the Sydney Technical College, Ultimo, Sydney NSW.
Still exists as the only complete Vengeance in the world.
It is based at the Camden Museum of Aviation at Narellan NSW.
Photo of 999
Hope is of help
Danny
Edited to add: I'm thinking the only fictitious part is the NH-Y identification. NH- was 12 Squadrons identifier.