If it's not an Apple drive, you would need to format it with the 7.5.3 Patched Image here:

http://maccaps.com/MacCaps/DIY_Information.html

Uniserver's drives really are pretty awesome. I have one and it's in my IIcx now, but I move it around. You may need a drive adapter to have it fit in your Classic II. I am not totally sure. But they are pretty cheap on Amazon or ebay.