Sorry mate thought this was another thread ive posted in that was similar, to cut a long story short.
You've unfortunately found yourself with possibly the worst skyline combo you can buy
question number 1... Are you on your Ps? If the answer is yes then scrap the whole thing as you'll require a mod plate instantly disqualifying you from legally driving it (regardless if its NA or not)
So you can't do any of the work yourself, this is a major disadvantage as a work shop is going to charge you $70 an hour just in labour alone before they ad parts on top of that.
....have a search around the place on here regarding (Natro) engine conversions I'm sure you'll find something.
(I have a feeling you'll be shocked by how much this will end up costing you if you went down this original route)
Rb20e to det swap: http://www.skylinesaustralia.com/forums/topic/418058-rb20e-to-rb20de/page__pid__6721237#entry6721237
Na+t conversion thread: http://www.skylinesaustralia.com/forums/topic/249186-nat-power-results-na-t-turbo-conversions-only/page__pid__6587345__st__140#entry6587345
Are they slow? (first few pages are relevant, the rest is rubbish, partially my fault lol) http://www.skylinesaustralia.com/forums/topic/417003-are-nas-really-that-slow-or-are-people-talking-out-their-ass/page__pid__6722430__st__320#entry6722430