I can confirm that Both Clover
http://ejie.me/And QTTabBar
http://qttabbar.wikidot.com/Are compatible with Classic shell and windows 8.1
And I personally use a combination of them. Though Clover can be somewhat unstable at times (the worst i've seen it do is occasionally crash the explorer, so you likely wont loose any data, and I doubt itl cause any permanent damage to your system) Its still the most visually appealing of the options
I can confirm windows tabs works (with classic shells explorer toolbar, and the rest of classic shells features), though I cant say about its functionality, or stability, as I haven't spent much time using it..
XYPlorer works with the start button, and Classic IE, but you wont be able to use the classic explorer toolbar in it
UPDATE:
Heres a pic of QTTabs working inside Clover inside Windows Tabs Allowing 3 tiered foldered tabs XD (not that anyone would ever use it this way, but it all seems to function properly)