Can't help on the main thrust of this, but can answer one question...

On Thu, Apr 18, 2019 at 8:33 PM <reed@reedmedia.net> wrote:
This email is two parts. I am researching 1970's symbolic name to
network address mapping routines.

1) I am looking for parsers for ancient (pre mid 1982) HOSTS.TXT. Since
this is Unix list, for Unix is fine :)

RFC 597 (12 December 1973) says a hostname list will be maintained at
the NIC with the location to be announced. (Interestingly NIC as in
FEINLER@NIC is probably a nickname as it is not listed in the host
status list. I am guessing it is a nickname for SRI-ARC or OFFICE-1.)

NIC is probably what became know as SRI-NIC in latter days. By the time I joined the internet in the early 80s, SRI-NIC was where you registered your domain name. I just missed the hostfile by a few years.
 
RFC 607 (January 10, 1974) the NIC agrees that NIC maintain a text file
of hostnames, addresses, and attributes. (It has also been suggested
separately.) The source is maintained in NLS format with multiple
attributes. (What is this NLS format?) A program could be written to
generate a weekly ASCII file. They will write the program and the
generated file will be at OFFICE-1 (IMP #43?) with pathname of
<NETINFO>HOSTS.TXT  (It's not Unix. It's TENEX I think. The ">" is the
directory delimiter, but what is "<"?)

It's TENEX or TOPS-20 (they are the same for this purpose). <DIR>FILE.EXT was the format. This was later extended to <DIR.SUB>FILE.EXT. So the <> just contain the whole path, separated by dots.

Warner