Based on the Joe Vella sideview drawing accompanying From Fisherman's Bend: CAC Projects, Proposals and Concepts (Air Enthusiast 1996-03), I'd guess that the P176 was to be fitted with a Double Cyclone (similar to the Wright GR2600-A5Bs planned for DAP Beaufighters).
Is XP17 the CAC project designation for the postwar HDH/GAF/CAC P17 jet primary trainer Vampire conversion? If so, the powerplant was to be a Bristol Siddeley Viper.
Source: The Age, 25 March 1964, pg. 5