Hello Jon, this forum is really coming along great, I'm so impressed by what you've achieved here. Keep up the good work.
With regards to the Terry Allan Camaro, and your questions about his choice of big block power, well, I can only guess. But another Australian sedan racer called Bryan Thomson, who also raced a big block Camaro in the late 1960s, had an interesting theory for choosing big block power. I put together a brief article on the Thomson Camaro on The Roaring Season a few months back, and here is what I wrote about his reasoning behind the big block motivation based on an article supplied to me by Chris Bowden, who at the time was selling the Camaro for owner Peter Sportelli:
"Thomson was from Shepparton, Victoria. His local race track was Calder Park, a 1.61km circuit with a fairly simple layout, containing four corners, linked by two long straights, and a couple of squiggles. The front straight doubled as a drag strip. So when Thomson found a 396ci big block powered '68 Camaro drag car being sold by local drag racer Neville Thompson, he pounced.
Norm Beechey held the Touring Car lap record at Calder, at 49.2sec. Thomson figured that as his Camaro could do 11sec ¼ mile times, and that as Calder was made up of two long straights, his Camaro, converted to road race trim, would be competitive. Not a particularly scientific approach, but a pretty good guess none the less".
The Thomson Camaro began life as a 396 car, but Thomson later had it fitted with a 427, which gave him 620hp, which, in 1969/70, was impressive for a road race car. Most small block cars in Australia at the time had around 450 - 500hp. Of course, as you've rightly pointed out Jon, a small block car will handle better than a big block car, but Thomson felt the extra power and straight line speed he gained could off-set the loss in braking and handling, and I can only assume Terry Allan was working on a similar theory. Of course, as history showed, both were wrong, the small blocks were better, barring Bob Janes alloy big block Camaro.
If interested, here is the article I put together on the Bryan Thomson Camaro: http://www.theroaringseason.com/showthread.php?324-Bryan-Thomsons-L88-Camaro