Okay,
I reinstalled Vienna Instruments Standard, which includes the reinstallation of Vienna Ensembe Standard. In my VST Plugins folder under VSL I now have the following files for Vienna Ensemble:
Vienna Ensemble.dll
Vienna Ensemble x64.dll
Vienna Ensemble x64.vst3
The first is the 32-bit version dll, and the second is the 64-bit version dll.
But the third is not a dll file at all. Clearly it is in some way related to VIenna Ensemble 64-bit and is connected with VST3 implementation, but what the relationship is, and what role the file plays is not explained.
When I open up the Plugin Information window the file name is listed as "Vienna Ensemble", the category is "Instrument", and SDK is "VST 3.02". Interesting that the file in my VST Plugins folder includes "x64" in the filename, but the listing here does not. Also listed as a separate file is "Vienna Ensemble x64" shown as a VST 2.4 Instrument, and this appears to be what is loading when I add instances of VE.
Anyway, when I open the VST Rack and see my options for inserting a 64-bit instance of Vienna Ensemble, all I see is "Vienna Ensemble x64," which is what I have been using all along when I insert instances of VE.
The plot thickens but still no answer.