the awd sump has different bolt pattern and oil pickup so you need to get an adapter plate
rips sell them, as do a mob in melbourne i think, there are a few about
some need external feed for the oil pump, some come with one that bolts in and around
cheapest option is probably pulling the motor out yourself, take it to a machine shop and go from there, just no way of knowing how bad it is till its open (and a pro inspects everything)
i'm back on the coast now if you want to chat, to be honest i've never built a motor but i've spent enough time reading though the forums to get a pretty good idea of what can/cant/should be done and rough costs
you can keep vct on an rb25/30 and its great if you can, r33 heads can be modified to keep vct really easily, neo heads seem to need an external oil feed
cost of the 4wd sump adapter is about $600-900 i believe
its a bit old but: http://www.skylinesaustralia.com/forums/topic/259282-gtr-rb30-sump-adaptor-plates/