There were definitely as many PDP-11's (most running UNIX) as there were DEC 10s in the glory days of the Arpanet. VAXes only rolled out toward the end of the NCP era.
However, the last NCP host table shows this statistic for DEC machines on the NCP Arpanet
VAX (UNIX): 58
PDP11(UNIX): 59
So as of 1980-12-31, you had 7th Edition and 32V in the wild. 3BSD was late 1979 or early 1980. 4BSD was late 1980.
The Columbus Unix was also running on VAXen, but I don't have great dates for that and most (all?) of those machines
were confined to internal AT&T.
I recall reading, but don't recall where I read it, that the Urbana networking was ported to 7th Edition. I tried to find
such source, but couldn't 18 months ago. 32V is basically the same as 7th Edition, so would make a good candidate
for such a port, though 3BSD isn't so radically different, except in buffer mapping, that it couldn't run there w/o much
effort. The VAX never had a V6 port that I've read about anywhere, though I'll defer to others with better sources.
I'd bet some $$$ that BBN did the port, but I have no good source for that either.
Warner