yeah its been done heaps both backyard style and workshops
for the specs read here
http://en.wikipedia.org/wiki/Nissan_RB_engine
but why would you take out your engine, buy a 2nd hand rb26 and fit that
it would not be worth the time and effort, for the power you'll get and the headaches/risks of a 2nd hand motor
if you were going to do it, it would have to a rebuilt rb26 so thats already a 10k cost (engine + rebuild)
this is why its far more reasonable to rebuild your engine, if you rebuild yours, you can pick what ever power you like