All, I had a look at the docs on V6 Unix. This doc:
http://minnie.tuhs.org/cgi-bin/utree.pl?file=V6/usr/doc/start/start
describes a way to install from tape, but it seems like it does
a block copy of a tape image to the disk.
Also, in
http://www.tuhs.org/Archive/PDP-11/Distributions/research/Ken_Wellsch_v6/
there is a v6.tape.gz file. Unfortunately, I have no documentation on this.
It could be raw blocks, or it could be a TAP file, who knows.
Hopefully this is of some help.
Cheers, Warren