For the archives:

I called Bus Depot, and they emailed me the following instructions:

"The thermostat has a cylindrical nipple protruding from it. This
nipple must be removed so that you can feed the thermostat cable
through the thermostat. This nipple is screwed on and also held with
sealant. You can carefully unscrew it, leaving a hole to feed the
cable through. Other than this difference, this thermostat runs a few
degrees cooler then the original one did (so your engine will run
slightly cooler), but the difference is not significant."

My observations: the nipple does screw off - the cable doesn't thread
through the thermostat, but I threaded it through the nipple and then
screwed the nipple back on. It works just like the "cable-holding cap"
that I saw on the original thermostat, except not as well :) It
doesn't screw all the way down onto the thermostat again, there are
quite a few threads still showing when the cable has been run through
it.

Cheers!
Mike.