By definition if it has a centre differential lock it's AWD, but we're talking about the rear diff. I don't know about Australia but here in Canada you could get a 5-speed RAV4 with rear limited-slip diff.
Mohit's a prime example of someone doing it right. Understandibly there's always questions with mods, how to do this how to do that...what are the benefits of this blah blah. But when the question can be answer yes or no by a simple phone call, go for it. It makes so much sense than posting up here on the forum where you're asking people that don't really know. And even if they're hunch is stronger than yours, you will still want confirmation.