Try this, google the difference between a centre diff and a transfer case. These guys know the car mate, it's clear your mechanical knowledge is a little way behind theirs. As for "bomb proofing" a gtr powertrain, put at least 40k aside. That's if you want to really do it properly. Lonefield billet cv's, billet driveshafts, carbon props hafts, hollinger sequential gearbox, quaife diffs front and rear, gts4 crown wheel and pinions, modified sump and front diff housing. Then you need to look at clutches, it gets out of control as while you make one thing stronger it creates another weak link in the chain.
There is GENUINELY bomb proofing as you say, then there is sensible strengthening of components