Nero the soecifics of Australian Formula Libre were that there were no specifics.
Libre of course translates as liberty. Ask an Australian to take a liberty and you can expect interesting results.
It was always a case of "run what you brung".
Pre WW2 racing in Australia was a rather amazing mix of Australian made specials and 4 or 5 year old pensioned off European cars. The usual form was to run either fully built up local race cars or imported sports cars with replacement bigger engines. A few Buggattis, things like Frontegnac Fords, the odd Lea Francis or Chain Gang Fraser Nash would compete with Ford V8 or Hudson straight eight specials. The first Australian GP by the way was won by an Austin 7 Special. Being a handicap event helped.
Following WW2 things took a while to get started again with much of the same machinery competing. A few Coper Bristols, a 4clt Maserati, an HWM or two and a couple of Lago Talbots came into the country but most racing was based around MG specials or localy designed and built cars featuring largish American engines. In the early 50s a summer series in Australia and NZ strated to attract som interest from British drivers and a couple of 4.5ltr Ferraris, superceeded by the World championship going to F2, were brought down, followed the next year by the first of the 250Fs.
The 1956 Olympic GP brought a couple of 250Fs for Moss and Behra with 300s sports cars to compete with the by then fairly strong local field of C & D type Jags etc in sports car races. At that time, even in Europe sports cars were dominant compared with the slower by then F1 cars. Many and various chassis were mated with modified versions of the Holden 6, with SV V8 fords, Jaguar, Hudson and later Dodge and Chev OHV V8s.
Probably the peak of the Austrlian specials were about that time. The Stan Jones Maybach, Ted Grays Tornado/Corvette are a couple tha spring to mind. There was even a special powered by a Lycoming Aircraft engine.
With the F1 spec from that time going to 2.5ltr a Tasman Formula of 2.7ltr
was adopted for the annual Australia/NZ tour and of Course Jack Brabhams influence ensured that initially Coopers, and later Brabhams were imported in some numbers to add to the machinery left behind each (antipodean) summer by the visiting circus.
JB by the way started in Speedway, moved on to an Ron and Austin Tauranac built Cooper JAP type unit, and then finaly before going to Europe a front engined Cooper Bristol run as the Redex Special.