The HK Monaro was updated quickly to address performance improvements in the competition so it came with a host of upgrades. This also makes the HK Monaro highly sought after because they were both very expensive at the time and were only made for eleven months. 

The 327 was replaced with the 350 Chev V8 and the Holden 253 and 308 cubic inch V8s were introduced.  HT Monaros were also assembled in South Africa and sold as the Chevrolet SS and were available with both the Holden 308 and Chevrolet 350 V8 engine options there.