Woops, few errors here with the engines. Let an old bugger sort you guys out on this one.
HK (1968 to 1969) 161, 186,186S, 307, 327.
HT (1969 to 1970) 161, 186, 186S, 253, 307, 308, 350 (The 307 was replaced by the 308 during the HT production run)
HG (1970 to 1971) 161, 186, 186S, 253, 308, 350
Shooter's car is a GTS and he mentioned that the engine is a 350 Chev - if it was an original factory built GTS 350, then it is a very rare and valuable item. The 161 and 186 could only be purchased in the base Monaro. GTS had the 186S standard, then you had the GTS 327 (HK) and GTS 350 (HT and HG). The base Monaro and the GTS could be optioned with the bigger engines up to 307/308, but the top of the range engines could only be purchased as a complete package. (ie you couldn't buy a base Monaro with a 327 or 350).
Shooter - best of luck finding that trim. It's definitely the way to go. Do you know of a source?