I meant to post this earlier, but another much more intuitive way to fix
the backspace (and any other keys, such as Meta) is with Jamie
Zawinski's XKeyCaps program.  It provides a graphical view of many
common keyboards, including the DEC LK201/LK401 and writes a file for
xmodmap automatically.

The program is available at: http://www.jwz.org/xkeycaps/

Just stick a command like xmodmap ~/.xmodmap-`uname -n` in your .xinitrc
file like it says and you'll never have to worry about the keymapping on
your pmax hosts.

Cheers,

JCSmolens

  /--------------------------------------------------------------\
 | Jared C. Smolens           Electrical and Computer Engineering |
 | www.rabidpenguin.org                Carnegie Mellon University |
 | jsmolens+@andrew.cmu.edu                        Pittsburgh, PA |
  \--------------------------------------------------------------/