Hello Mouse!

  dM> There is a bank of fans (9? 12?) at the bottom of the
    > cardcage that pulls air down over the cards and out
    > the bottom.

That's curious, why fight the natural inclination of warm
air to rise, when it could actually help?

  dM> I installed an airflow restrictor (a blank sheet of
    > metal that slides into the board guides) in the slot
    > next to the CPU, then laid pieces of paper to block
    > the airflow to the right of it.

I've seen something similar used in racks before, it seems
sensible.

  dM> I think I've lost at least one CPU board to
    > overheating, and come close to losing others.

I wonder if the 3/110 style case is any better in that
respect.  Anyone know?

  dM> Overkill Is Your Friend.  Especially when trying to
    > keep ancient hardware going. :-)

<grin>

  dM> (I want to move the functionality that -3/60 is
    > supporting to somewhat more modern hardware...

I was looking earlier today at 3U 680x0 based VME cards,
which should be faster, more robust and less thirsty.  I'm
not sure I have sufficient knowlege to run NetBSD on them
though, and they are a heck of a lot more expensive than a
3/60!  :-)

Regards,
  - Andy.