I just upgraded my fronts with Sutimoto 4 piston calipers, can get them off R32 gtr or Z32 300zx (with cooling fins) or off R33 (No fins), the fins make no difference, I found that they fit perfectly on my S1, just had to remove a little orifice from the fluid inlet and I was able to use my standard brake lines with banjo bolt,
to remove the orifice basically get a corse screw and screw it in and then use a claw hammer to pull it out
give the aus300zx forum a look, those guys sell there calipers alot cheaper than the R33 guys, I got fronts with good pads and with DBA4000 slotted rotors for $200,
the calipers use DB1170 pads which are pretty much a standard shelf item in most car shops that ive been in
P.S while your looking at changing them out give them a splash of paint, works wonders in the looks department.