Charlie, there is some interesting history of the pre-RS/6000 AIX
stuff here (you give a quote :)). Particularly page 41 gives a
chronology of UNIX at IBM:
https://amaus.net/static/S100/IBM/RTPC/AIX%20Family%20Definition%201989.pdf
Prior to AIX the Series/1 had a UNIX port in the early '80s. I think
that work happened in Boca Raton.
FYI: the original S/1 port was done at Cleveland State with the Seventh Edition - the name of the Prof that led it I can not say I remember nor his HW configuration, but I do remember his presentation. It is where the term 'NUXI' was coined. I want to say in 1979 or 1980, they gave a wonderful talk about it. They had some help from folks at Case as they did not have a PDP-11 of their own and never seen UNIX before (i.e. they arranged to borrowed time on a PDP-11 at the EE Dept at Case. They wrote a new back end for the Ritchie C compiler, and recompiled everything, wrote new drivers for the S/1 HW and rewrote m40.s as needed. Then they wrote the disks, then drove the packs back to Cleveland State. IIRC it took a summer of work to complete).
FWIW: The PDP-11 has an interesting way it does byte-swapping and when they first booted the system, the first message was NUXI which was how the S/1 saw the strings. The term was used from then on in the community to describe byte-swapping issues.
I remember all of us in the audience howling with laughter when they described their work. Unfortunately, this was before USENIX kept conference proceedings so I'm not sure if the talk and paper were archived.
And the truth is, I wish we had that port in the TUHS archives.