Also they don't like to rev - see Lewis engines page on harmonics and not revving past 7500 and oil pump failures http://www.lewisengines.com.au/rb-tech/
For the least headaches, source an RB25t and start by getting it cleaned and machined. These motors can make big power and cheaply, as many want to do an RB26.
Nick's right. The machining costs alone are astronomical. It has been done time and time again and the results quite frankly sucked.
You can't have turbo compression on an n/a built motor either, the thing would be a pig.
He ended up stripping it down and selling everything http://www.skylinesaustralia.com/forums/topic/418407-rb30-with-nitto-32-short-motor/?hl=%2Brb30+%2Bstroker+%2Bna