At some point, Unix V7M was rebranded as Ultrix-11 and pulled in a lot from the BSD releases (2.9 or 2.10) to get TCP/IP
networking onto the PDP-11. I don't think DEC ever shipped pure AT&T binaries. The V7M was a modified version of V7,
with most of the modifications in the kernel to fix a few bugs with buffer handling, and also make it run on all the different
PDP-11 models.
All the sources to V7, V7M and the last Ultrix-11 version are in TUHS for people to peruse...
Warner