Well i agree with drift freaq in the fact that it would be a ton of money,but I think it would be real cool to do the rb30. IIRC you need the entire short block, from what ive read i dont think they can fit in S13 or S14 with out custom mounts or notching of the hood as they gain the extra cc's with stroke not bore. imight be wrong but the best thing to do would be to check out
www.skylinesdownunder.com if you want good info and they usually have a ton of rb30 blocks for sale as they're quite common over there. Good luck with what ever you do.