the R33 caplipers have a different sized bolts that bolt them to the hub, the S2 stagea ones are too big for the R33 brakes, from memory the stagea ones are M14 and the R33 M12.
to bolt the R33 GTST calipers to the S2 stagea hub you'll need to get some longer bolts that suit the R33 calipers, as the R33 bolts aren't long enough to get through the thicker stagea caliper mounting plate on the hub. you'll also need some sort of bush to help locate the M12 bolt in a 14mm hole, i am going to turn up a bush on the lathe when i finally get around to doing it, but i've heard of someone using a small piece of copper pipe.
i haven't looked into the rotor side of things yet, one thing i can tell you is the stagea rotor cant be used with the R33 calipers. i have some R33 GTST calipers in the garage and had a look one day at what was needed to put them on, i also have a S2 RS four V. and thinking of it now the only thing i didn't check was to see if the brake line fittings were compatible.