a few things to clarify
NISMO DO NOT MAKE an N1 Block
NISSAN make the N1 block. It has a higher Nickel content than the Standard RB26 Block and is stronger.
NISMO just realeased their GT Block this year to co-incide(spelling??) with the release of the R34 GTR Z tune. It is the same block used in the GT500 Race Cars.
Gav, increasing the bore size helps you increase the displacement in the engine. Hence why the HKS 2.8L Kit uses 87mm Pistons.
Retaining the original bore size or only going to 86.5mm pistons aids in developing fantastic engine response (not something that is overly focused on in drag setups). Also going to an 87mm bore rasies concerns about the overall strength of the block. It's fine if you run a drag car that gets re-built often but for a street car that need to last, it's an unnecessary risk IMHO.