which makes sense to me. S1 RB25 went both ways . non VCT and VCT. mine is a S2 grey plug ECU. in my case was mated to an automatic box. the grey plug ECU does the auto box control and engine control all in one. the extra harness on the S1 engine was usually for the automatic box controller.
can't use 15" wheels. I have big brakes under mine. min 18"