[techweenie]

If the offset and size are the same on both rear wheels, there is likely a chassis tweak.

I had that on a 73 many years ago and discovered the torsion bar tube was bent, despite no visual indication of chassis trauma. That is not an easy issue to tackle, and in my case, it was a low buck track car, so I had my alignment shop bend the spring plate to compensate for the angle of the torsion bar. Worked fine as a 'field expedient' fix.

Anyone who has been around 911s a few decades has run into the differing positions of wheels in the rear - and to some extent in the front. In my experience, it's always related to chassis "history."