i know using 33 or 34 PFC you need to change a few things, maybe it is as simple as that to use a 34 stock ECU, or less again to be changed for a s2 stagea... might be best to speak to a tuner...
z32 runs a 33 RB25, with minor wiring changes, dunno if anyone has run a 33 with a 34 ECU for example...