using installation tape for disaster recovery

[rusty wright]

I'm trying to reinstall my system from dump 0 tapes using the
installation tape.  (In case you're wondering why, I tried to install
Ultrix 4.0 on my MicroVAX II/GPX and found out after it was too late
that 4.0 won't work on an RD53.)  When you boot the installation tape
there are 3 options, basic installation, advanced installation, and
system administration.  If you select system administration you get
dropped into the shell on a unix running on a ram disk.  My confusion
is that only mkfs is provided for initializing the disk, not newfs,
and it's newfs that installs the boot block, so I don't see how I can
install the boot block.  Can anybody enlighten me?