the reason we have such great import laws is because Japanese imports were damaging the aussie car market sales so Johny introduced more tighter laws which also added to the price of importing.
the main area's that need work on a rwd ceffy is that trans tunnel, the front struts and front chassis, as you need to panel beat the the trans tunnel, as well as needing modified box cross member , modify the front chassis rails for the front half shafts( and maybe for the gts4 eng cross member too?), and modify the front struts to bolt on the front suspension assembly.
the rear can be left alone if rear diff ratio's aint a worry, unsure if a custom/ modified tail shaft is needed or if it will bolt up to a ceffy diff.