I haven't read any of this thread, and i'm not sure if anyone has mentioned this, but i'm using R31 strut, R32 280mm disc and R32 4 piston caliper. Its overkill, and also leaves me the option to swap to GTR 297mm (lol) if i got bored without changing any of the setup bar the discs and calipers, bolt on swap. Going to write a guide for this but haven't got around to it.

Alternatively use the R31 strut and discs complete, they'd probably do the trick and would be considerably cheaper. Need to change spring seat / tops / etc obviously though.

Search for posts by me with a few keywords on this if you're interested, i've gone into more detail a few times.

ed: lol just read the 12" or 13" wheel bit, oops

Stock R31 might fit under a 13 or 14?