I don't really know much about the regs down under but all three motors are capable of plenty of power and reliability. I wouldn't reckon on an FJ20 in N/A form and I think it would be
difficult to fit in a turbo version. I have just got an FJ20DET and it's huge compared with a CA18. Really it's just down to CA or SR. SR is probably gonna be lighter but I'd reckon a CA
would be easier to fit. Which ever route you go there are people here who have been there before so will be able to offer their wisdom. Given the choice I'd go with an SR20DET if you can
get one for sensible money. Have you checked out the SR 1200s on Autospeed? http://www.autospeed.com/members/A_0420/article.html

Good luck,
Eddie