The AUSubaru.com.au Forums

is this difficult and what parts do i need?

Its a pain in the arse!!
it's not that difficult just you need to have all the bits:-

AWD fuel tank
AWD complete rear suspension, Diff hanger & hubs...

It can be done, the value of your job would be same price as if you're buying an AWD Liberty.

All you need is AWD fuel tank (it will have dual fuel sensors - whereabouts FWD has one sensor), rear suspension, rear diff, drive train, rear CVs, axles etc... plus plenty of your time to install it! If you're gonna ask a mechanic to do it for you, you're wasting your money! A lot of people have done this, there is a forum called USMB Subaru in North America that has done this kind of project.. I personally would go for it if I could find these parts easily!

Cheers
AP