He means the twin cam head obviously is a shitload better than a RB30 head.
Therefore as I said, if you were going to all the effort of putting a RB30 into a Skyline you would build a RB30/25 or a RB30/26. Look, we have a whole forum section dedicated to it:
http://www.skylinesaustralia.com/forums/forum/184-rb30-conversions/
What are your reasons for wanting a RB30 SOHC in there when it is a worse engine than a RB25 or a RB26 and a hell of a lot worse than a RB30/25 or a RB30/26?