I just did a fresh OS reinstall and downloaded the latest UAD software. Sure enough, there were no mono versions of the plugs in there.
 
Looking around the web people seem to be saying mono plugs were dropped after driver v6.3.2, while 64-bit was introduced at v6.4. 
 
But I definitely have projects on my disk containing mono instances of 64-bit UAD plugs! I'd really, really love it if someone could tell me what I need to get those projects up and running (and, I'm hoping, tell me of a way to find the right UAD software version...)!
 
Sven

Fixed! Seems the UAD installer puts the mono versions in the good ole C:\program files\steinberg\vstplugins\ folder and the stereo ones in c:\program files\universal audio\. Just a matter of including the Steiny folder inside SONAR (and then knowing where to find them in the plugin menu).
 
UAD could've included folder options in their installers!
 
I used the v.6.5.2 driver version from:
www.uaudio.com/support/uad/archives.html

Glad you got it sorted out Sven!