V6, as distributed, had no networking at all. There are two V6 systems with
networking in TUHS:

 https://minnie.tuhs.org//cgi-bin/utree.pl?file=SRI-NOSC
 https://minnie.tuhs.org//cgi-bin/utree.pl?file=BBN-V6

The first is an 'NCP' Unix (unless unless you have an ARPANet); the second is
a fairly early TCP/IP from BBN (ditto, out of the box; although one could write
an Ethernet driver for it).

I’ve also done a port of the BBN VAX stack to V6 (running on a TI990 clone), using a serial
PPP interface to connect. Experimental, but may have the OP's interest:
https://www.jslite.net/cgi-bin/9995/dir?ci=tip

There's also a fairly nice Internet-capable V6 (well, PWB1, actually) from MIT
which I keep meaning to upload; it includes SMTP, FTP, etc, etc. I also have
visions of porting an ARP I wrote to it, and bringing up an Ethernet driver
for the DEQNA/DELQA, but I've yet to get to any of that.

I’d love to have a look at that and compare and contrast the approaches.

I’m finding that BBN’s original design, with a separate kernel thread for the network stack,
is elegant but difficult to tune: too much priority and it crowds out user processes, too little
and the slow PPP line is not kept busy.

I think I’m beginning to understand why CSRG (and later also BBN) moved to
the interrupt driven structure of 4.2BSD: perhaps it was also difficult to tune for a
VAX with ethernet.