I wonder if this is an early predecessor to the overlay stuff in BSD 2.9 (and
later BSD's)?
Unlikely. The BSD overlay stuff was based on Fred Cantor work at DEC in the TIG group in Merrimack, NH that did V7m and later Ultrix11.
Fred's code works on 11/40 as well as 11/45 class processors, where as by the time of 2.11BSD they dropped the 11/40 support.