Thanks Jon, very much appreciated. Further to my post above on terry Allans Camaro, when looking back on Australian touring car racing during the 1960s, and from when the Australian Touring Car Championship (ATCC) first began in 1960, through to the end of the decade, there is a quite clear historical line that shows Australia was enjoying something of a horsepower race. The ATCC from 1960 - 1968 was held as a single race event, then became a multi-race series from 1969 onwards.
The 1960 - 1963 ATCC was dominated by MkI and MkII Jaguars, and Bob Jane was comfortably leading the 1964 ATCC when his Jaguar was struck by clutch problems. By 1964, the engine in Janes Jag was stretched out to 4.1 litres. Then, in 1965, Norm Beechey showed up with the first Mustang to race in Australasia, but as Australia was a country largely dominated by British cars, as its own local manufacturing began to gain momentum, many cars that competed in Touring car racing at the time were British, bar the local six-cylinder Holdens, but these were no match for the Jaguars.
When Beechey imported his Mustang, there was plenty of interest in the car, but also plenty of sceptics, because, in this part of the world, this was something of an unknown, and there were very few people who specialised in American V8s. But Beechey quickly began winning races, and both Bob Jane and Pete Geoghegan soon imported Mustangs of their own. Beechey won the 1965 ATCC, and from that point American V8s became the weapon of choice.
Geoghegans Mustang became the dominant touring car in Australia throughout the latter part of 1965, and into 1966, so Beechey decided to go bigger, and imported a 327ci Chevy Nova (Chevy II). Geoghegans Mustang was thought to have 360hp at the time, whereas the Nova was said to have 450. With this, he built a big lead in the 1966 ATCC at Bathurst, until his 4-wheel drum brakes slowed him towards the end, and Geoghegan moved ahead to win. But the Nova had proven how effective big cubes were.
In early 1967, when Terry Allan ordered his Camaro, the Camaro as a road race car was still a relative unknown. It took Mark Donohue until August 1967 to win his first Trans-Am race with the Camaro, and as Australia was heading fast-forward into a horsepower war, Terry Allan possibly thought he could get the jump on other competitors, by going straight to a big block. Teams in Aus were still learning how to make an American car handle well, the small capacity Mini Coopers and Lotus Cortinas could still beat them on somel race tracks, but big power could be had relatively easy by going for big cubes.
Australia at the time had a touring car maximum engine capacity of 7,000cc. Quite why Allan didn't fit his car with a 427, I'm not sure. Its possible the Confederation for Australian Motor Sports (CAMS) made the decision for him, as they accepted or rejected what cars could actually compete in touring car racing, eg, fastback Mustangs were not allowed, until 1969, Porsche 911 racer Jim McKeown wanted to race an AMC Javelin in 1972, but CAMS stopped him. Their decisions were likely based either on what had been sold in Australia at the time, or international build numbers.
I guess with the benefit of hindsight, a Bill Thomas 327 punched out to 377ci would have been a batter option. Thomas was apparently getting 520hp from his 377 motors when building and selling his Cheetahs in 1963/64, and Allan was only getting this much power by 1969 in his 396. But the big block probably appeared the best horsepower option at the time he ordered his car. But what I don't understand is why he stayed with the big block throughout the next four years when this option gave him so much trouble.