Just a thought but:

The upper ground glass would be very close to the focal plane in the neg
carrier, it would be almost or when stopped down in focus.  Therefore the
'grain' of the frosted surface of the glass would show up on the print.

Just a thought, not tried it.

Pete

Depth of focus. You really don't want to be focusing upon the confusion of
the ground-glass above the negative.

If you want to try diffusion "on the cheap" put the ground glass at least an
inch above the negative stage but below the condensers, you may need to rig
some sort of spacer to get the job done.  You'll lose a lot of printing
speed. And Opal glass works better but you'll lose even more speed.

--
darkroommike

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hi steve-

i worked darkrooms prof for almost 20 years.  i have used such an apparatus.
it is very finely ground glass set into the carrier so as it is hovering
slightly (maybe 1/2 inch) above the negative that is sandwiched in 2  other
pieces of glass.  it's a built in diffuser, really.  i used it only on 4x5
negs, but i think the same principle would apply to any size - IMHO.

mike posted a good solution.  it may take some rigging, but you could make
one out of an existing glass carrier without too much of a hassle.  i found
the extra exposure time helpful also, esp if working with a bad neg, as so
many of my printing jobs were - people who don't know how to expose film
properly.  and the diffusion of the harsh light of a regular condenser head,
which i use at home now, is nice too.
there's nothing a small set of screwdrivers, black tape and old carriers
bought a flea market can't do, really.
give it a shot!

-c.