All, I'm not sure if you know of Walter Müller's work at implementing
a PDP-11 on FPGAs: https://wfjm.github.io/home/w11/. He sent me this e-mail
with an excellent source code cross-reference of the 2.11BSD kernel:

   P.S.: long time ago I wrote a source code viewer for 2.11BSD and OS with
      a similar file and directory layout. I made a few tune-ups lately
      and wrote some sort of introduction, see
           https://wfjm.github.io/home/ouxr/
      Might be helpful for you in case you inspect 2.11BSD source code.

Cheers all, Warren