I don't know what a drive letter is but I'm assuming it's the letter next to the sdcard's name in parenthesis. It's (F:').
I think you're confused.. sorry if I'm wrong but the savedataback folder is on the root of my SDcard. Or are you talking about the save_manager folder that has save_manager.3dsx, save_manager.smdh, etc. ? That's supposed to be in the 3ds folder right?
edit:2. Sorry, it's almost midnight for me and I'm tired. I'll try to explain as best as I can. a pk6. file, bin, etc. is on my desktop. when I try to drag the file to pkhex, it doesn't load. instead, it shows a red circle-backslash symbol/universal no (http://www.clipartkid.com/images/460/circle-slash-symbol-free-cliparts-that-you-can-download-to-you-KlNjMT-clipart.jpeg) and doesn't allow me to put it in.
3. I guess I'll have to deal with that