>    How expensive are those National chips?  Anybody have the part number
> handy?

The commonly used part was a DS3662 four-bit transceiver, which was an
improved-spec version of the DS8641.  Both were obsoleted last year.

National still makes an eight-bit version, the DS3862, but has announced
an end-of-life for that as well.  It will be available until the end
of 2003.

I am unaware of any other transceivers or drivers that can meet the
Qbus/Unibus/Omnibus electrical specifications.