A1264 is indeed supported by Mavericks and AirPort Utility 6.3.2.
Not sure what the issue might be if you cannot "see" the devices in AirPort Utillty.
You have "hard reset" the A1264 by powering it on for a few minutes, then holding in the reset button for 10 seconds, releasing and allow a full minute for the Express to restart.....correct?
Restarted your Mac?
Wireless is turned on at the Mac?
Temporarily connected an Ethernet cable from your Mac to the Express?
If nothing works, try the steps in the Apple Support document, then repeat the steps above.
Great, I didn't realize I had to have wireless activated on the mac--after all it is connected to the network already via ethernet and I figured since the connection being sought was between the Express units and the Time Capsule--this setup would be independent of the Mac's wireless capabilities. Anyway, a simple solution--thanks!