I downloaded and installed the ProChannel Concrete Limiter, but can't seem to find it anywhere in the browser.  I assume it would be in the Audio FX tab somewhere in the VST2 folder, but I can't seem to locate it, and a Windows search only locates the setup.exe file.  Any idea where the plugin could be?  Thanks a lot!

Pro Channel
In console view, on your tracks, you will see 'PROCHANNEL' with a little arrow beside it, click that arrow and the Prochannel will become visible, you may have to right click, select 'Insert Module' and selct 'Concrete Limiter"
Or in the Inspecter view, just select the 'ProCh' tab at the top.

it installs here: C:\Program Files\Cakewalk\Shared Utilities\Internal\ProChannelConcreteLimiter
 
 . . . but because it's a exclusively a prochannel module, you can't drag and drop to an FX bin

Wow, I never realized that certain ProChannel modules were not also found as VST plugins.  Well, I found it, so thanks a ton!
 
On a somewhat related note, the Ca-2a appears both as a PC module as well as a VST3 plugin.  Is there any advantage to using the plugin in one way versus the other?

No, not that I am aware of.