Thats not the biggest problem. I wish that that was all I had to do.
The legs on the Sumitomo calipers are too short (in radius) meaning even dummying the calipers in place, the 297mm rotors are too large for the calipers suited to them (on the R33, but on the S2 Stag they don't work). I even toyed with dummying in place the 280mm rotors and the calipers still fouled on the rotors (even when I spaced out the offset).
So the R33 GTST calipers and 297mm rotors have the right offset, but totally wrong radius (by about 20mm); and
The R33 GSTS calipers and Stag 280mm rotors have the wrong offset, and still wrong radius (by about 3mm).
Something to do with the 14mm bolt pattern for the calipers being close to the centre of the hub.
Well I'm screwed now, because I had a time attack in 3 weeks, and a brake upgrade that isn't working and I've blown money on it already.
I'll give the guy you mentioned a go.