Where did you find the BBN TCP/IP stack?
Easiest place to find it is the TUHS Unix Tree page:
https://www.tuhs.org//cgi-bin/utree.pl?file=BBN-Vax-TCP
Several tapes of it survived in the CSRG archives, currently held by the Bancroft Library
at Berkeley.
A late version of the tcp/ip routines survived at the Stanford SAIL archives, currently
online here:
https://www.saildart.org/[IP,SYS]/
(mixed in with sources for WAITS).
A much evolved version is in the BSD SCCS history:
https://github.com/weiss/original-bsd/tree/master/sys/deprecated/bbnnet
Note that the location ‘deprecated’ is where the code ended up. Back in 1985 it would have
been in the normal build path, but SCCS does not preserve that.
Paul