and only slightly modified
You read some BS in here ...............
http://www.youtube.com/watch?v=Ng3EWIDaJ-QIt was produced at a time when neither Britain nor the US showed willingness to provide Australia with aircraft for defence. This was right at the start of the Pacific war, Australia's Army, Airforce and Navy were pretty much all in Europe leaving nobody at home to fight and nothing to fight with. There was not a single fighter aircraft available. The production of a fighter had been part of a longer term plan of industry development but nothing tangible had come through.
As it had to be manufactured from nothing, almost overnight, as many "off the shelf" components were used as were available. CAC were already making the Wirraway advanced trainer (which did shoot down a Zero btw and was the primary defender of Rabaul) so they saved time by using what was already in the parts bin. It had commonality in a number of parts, but not much else with existing aircraft. For example, it used the same engine as the Wildcat but that hardly qualifies it as a "modification" of the F4F. It was a fresh design. It was a credit to Wackett and David. It flew, it fought.
A "handy" fighter resulted, but one which had no supercharger and thus no high level performance. This was rectified in the later marks but few of those were produced.
Entreaties to Washington paid off (backed up by Macarthur and especially Kenney) and a useful number US aircraft started to flow south. Churchill wasn't happy about that btw and Australia historically realigned to a pro-US stance and has stood there ever since. Britain also came to the party providing initially Spit 5s and eventually new-build Spit 8s. Boomerangs simply couldn't match the speed and height of Japanese bombers hitting Darwin but were used for local defence at forward fields like Millingimbi and Horn Island.
http://www.youtube.com/watch?v=cd8C7-OJFVchttp://www.ozatwar.com/airfields/millingimbiairfield.htmContracts allowing CAC to manufacture the P-51 locally eventually pushed it off the assembly line but its replacement was kept under development until the end of the war "just in case". This was the CA-15 which remained a continually updated paper project until the war finished at which time a single copy was built.
http://www.adf-serials.com/2a62.shtmlThe nakedness Australia felt so keenly in late 1941 led to the insistence by succeeding Governments to maintain the ability to manufacture fighter aircraft here since that time. This policy is only now under scrutiny and review - 70 years later.
CAC have manufactured under licence such types as: P51 Mustang, Avon Sabre, Mirage 3 and F/A-18.
This link is just for those who like the sound of loud (even distorted) radials:
http://www.youtube.com/watch?v=y72xQ11ekGw&feature=related 
