Thanks to all for the input! The top fastening option looks like it
will actually work vs going into the concrete.

Originally I didn't think the shelves in question would be tall enough
for that to be practical without a long awkward run of cable or
something, but there really isn't that much distance between the top
and the sill plate on these 72" shelves. Now that they're up, they
also hold together vertically better than I originally envisioned.

Best regards,
--
Todd H.
http://www.toddh.net/