A couple more options occurred to me after I posted.
On 2015-12-04, Will Senn wrote:
1. a utility on the host that is capable of copying a
directory and its
contents, recursively, onto a blank magtape/dectape/rk image that is
then readable in the v6 environment
Maybe run tp in apout? Actually, V7 through 4.4BSD has a tp that is
written in C. Maybe see if you can get it to compile on a modern system.
4. some kind of directory transfer utility that works
over telnet that
can be executed from a FreeBSD or Mac OS X host and that can be executed
on the v6 system as well.
Well, you could try to make one using rcp as a starting point.
Or send a shar to the terminal to be executed by an interactive shell.
(I make no claims about how well typical shar archivers work with the v6
shell and utilities; you might have to write one.)
5. a utility capable of creating an empty
magtape/dectape/rk image and
another capable of making a filesystem on the image and another of
populating the image (analogous to fdisk rkimage; mkfs rkimage; rkcopy
dir rkimage)
AncientFS is read-only, but adding write capability might be an
interesting project.
http://osxbook.com/software/ancientfs/
http://osxbook.com/blog/2008/12/22/ancientfs-on-linux-and-freebsd/