The hubs should be the same, but I have a similar issue but less pronounced, when my top plates are set to identical marks, the passenger wheel pokes more than the driver side. Since your driver side is my passenger side, it makes me wonder if either of our cars aren't tweaked a bit from being driven mildly into curbs and such... yours would be on the opposite side of mine because of the different driver position. My side to side difference is minimal so I just used my top plates to adjust, but I haven't taken the car to an alignment shop yet to see. It wouldn't be the first time the front end of an S12 was slightly irregular, yours could just be worse than others.
Also, something to note about pattern parts... we don't have this problem here as much in the States, but from what I understand, pattern parts in the UK are often made with really shitty quality control. It's not uncommon for a pattern fender to not line up at all, or for a pattern engine accessory to not fit right. You could have a control arm that is DEFECTIVE! In the end, a factory original arm would be best if I were going to get a part for a car there.
Common fitment for S13 conversion depends on what arm, not on what hub. Oh and of course the wheel
But your wheel is actually reasonable offset. S13 arms are longer than S12, and S14 arms are longer than S13. I usually suggest to people that if you don't want to deal with camber issues, use S12 arms. S12 arms.
Not sure that answers your question exactly but hopefully it raises some thoughts on the situation.