The October 1984 BSTJ article by Felton, Miller and Milner
https://www.bell-labs.com/usr/dmr/www/otherports/ibm.pdf
Describes an AT&T port of UNIX to System/370 using TSS/370
underpinnings as the "Resident System Supervisor" and used as the 5ESS
switching system development environment.
I also found mention at http://www.columbia.edu/~rh120/ch106.x09
chapter 9 of http://www.columbia.edu/~rh120/ with footnote 96:
Ian Johnstone, who had been the tutor at University of New
South Wales working with Professor John Lions, was one of the
researchers invited to Bell Labs. He managed the completion at
AT&T Bell Labs of the port of Unix to the IBM 370 computer. See
"Unix on Big Iron" by Ian Johnstone and Steve Rosenthal, UNIX
Review, October, 1984, p. 26. Johnstone also led the group that did
the port to the AT&T 2B20A multiprocessor system.
I found
https://ia902801.us.archive.org/3/items/Unix_Review_1984_Oct.pdf/Unix_Review_1984_Oct.pdf
"BIG UNIX: The Whys and Wherefores" (pdf p.24), which only offers rationale.
Also:
"IBM's own involvement in Unix can be dated to 1979, when it
assisted Bell Labs in doing its own Unix port to the 370 (to
be used as a build host for the 5ESS switch's software). In
the process, IBM made modifications to the TSS/370 hypervisor
to better support Unix.[12]"
at https://en.wikipedia.org/wiki/IBM_AIX#cite_ref-att-s370-unix_12-0
Is there any other surviving documentation about the system?
Any recall of what branch of AT&T UNIX it was based on?
[ since this original question hasn't been answered ]
V6. There were 3 v6 ports: two interdata ports (Wollongong and Labs) and one VM/370 port (at Harvard or Princeton). They are got to first boot the sane year, within a few months of each other
Uts grew out of this early port. There's several blog posts about this and the TUHS archive has the initial port that was recovered from DECtapes recently.
AT&T also did a V7 port, which I think is what is written up in the bell labs journal. I'm not sure I have a proper source for this other than comparing the two accounts. I don't know if research did this or another group.
AT&T did the VAX port of V7 called V32, but v32 was little more than a swapping kernel that didn't do demand paging. This is where the Berkeley folks started to do paging with 3BSD. It is also where AT&T did their Vax port that other mailing list threads chronicled.
Warner