[rescue] OT: Antenna mounting to existing steel?

[rescue at sunhelp.org]

Need help from the ham/antenna enthusiasts on the list
of a small project.  I'm going to be mounting a BAE GPS
Receiver (the "Smart Antenna":
  http://www.navtechgps.com/supply/smartant.asp )
onto the roof of the converted warehouse we use for offices.
The receiver claims "easy pole mount" and someone
who has one has already told me that it uses a standard
mount.  Since I know next to nothing about civilian
antenna mounts, I need help.

1.  Any suggestions as to how best to mount this thing
   to an existing horizontal steel I-beam (roughly 6"x6"
   cross section)?  The I-beam is left over from previous
   HVAC equipment, and it means we don't have to create
   our own structural anchor point--but I'm not sure how
   much of a pole I need, or what sort of a base I can use
   to anchor that pole to the I-beam

2.  Any suggestions for local (Maryland, between DC and
    Baltimore) suppliers to procure mounting parts?  I'm
    sure that Dave M has a favorite ham supply store in
    the local area.

On a related note, once this thing is up-and-running for
it's primary purpose (GPS-related "location authentication"),
I'll be working on setting it up as one input to local NTP--
which dovetails with some other recent discussions.  I
may be asking for hints on that.  I *really* want both
Rb and Cs frequency standards so I can convince myself
that I'm back in the Commo shack, but the budget doesn't
permit...

Any help appreciated--thanks!  (Unless you think your
response is of general interest, probably best to reply to
me off-list--I'll summarize to the list if it seems warranted.)

  --Rip