Thanks for the help, everybody! I now have Field of Glory II running as I would like, in a custom folder/drive, and with Mods installed and accessible to the game in a custom folder too.
For those interested in why I might have had difficulty:
1) I had no trouble with installing the game to a custom drive/folder
2) The problem was an apparent requirement of having the game Mods installed into a folder which was by default on the system drive/C drive/fast drive.
3) The solution I was hoping for was for the game to be updated to allow you to specify where this default folder would be found. The solution was instead to relocate the needed folder from my system drive to a storage drive. (I think my solution would be more elegant, but would require coding.)
4) Compounding the confusion for me was hearing that the TT Mod had to be in that default folder. (It is the largest Mod, also.) This made me think that cutting pasting the folder elsewhere wouldn't work, as it would no longer "be the same folder", as it would then be in a different location. Fortunately, if you take a man full of beer out of a bar, he remains, in addition to being full of beer, the same man.
5) I didn't keep documents in that fast drive folder, I just kept the folder as I believed it was necessary for the game's mods to work.
I am happy to be able to enjoy the game again.
Zakblood's instructions solved it:
Right-click the My Documents or Documents folder. ...
Click the Location tab.
Click the Move button.
In the resulting dialog box, go to your name folder in drive D:, create a new folder inside it called documents , and select that.
After you click OK, click Yes to move your files.