SK;
the people from whom I've sought advice, in suggesting that there are 'little things' you have to get right on a road car including those you've mentioned (wouldn't I have to change diff ratios and speedo recal with an RB30 anywayas it revs lower?) also suggested that there's a lot of machining work to be done - far more than a good RB26 build. I've read the RB30 thread and buggered if I can really see it but that might not mean much either. As I said it's difficult to find and gte access to people who have done this conversion on a GTR. AVO couldn't even give me a ballpark on the phone, I had to call them back a week later.
re block issues, there are two things that I understand can be a problem. one is cracking due to greater torque/ torsional stress in a 4wd (they had no concerns in a 2wd) and the other, as Dror has found, is the $ to address this issue. which leads us back to the issue of 'while you can do it not everyone can, but you can't build me a motor and the people that we have access to, and can, want huge $'.
yep I'd love to try it because I agree it makes such good sense and the torque - presumably - is quite awesome but at this point, for a 4wd road car seeking to make about 400 rwkw it doesn't seem viable/worth the angst to do the conversion.
Cheers