Thank you salo and Hubert (and everyone else who replied).

I used the sparc disk1 and disk2 floppies to boot, escaped to the shell,
and then mounted the disk. (I did not fsck the disk as it suggested.)

Then I used ed (and vi[1]) to modify: shadow (to remove password),
resolv.conf, hosts, defaultrouter, defaultdomain (made it empty), nodename
and netmasks.

Well it works now: it gives me a login prompt via the serial console and I
can login.

Later, I may write a brief comparison of SunOS 5.5.1 with NetBSD.
Then I'll run NetBSD on the hardware.

Some of my miscellaneous and unorganized notes are at
http://www.reedmedia.net/misc/netbsd/sparc.html

Thanks again,

   Jeremy C. Reed
   http://bsd.reedmedia.net/

[1] vi and less are messed up, probably because my TERM is wrong: I am
using a serial connection with cu in an rxvt window with the TERM set to
xterm.