ZIF (45 pin generally) is electrically compatible, but given that it has less pins, a simple converter is out... and ZIF drives tend to come bare, ready to plug into a flex sporting system.

I think you're likely to be limited to a drive of the same connector type. Not sure what the drives are in the iPod Classics, I can take a look today. If your 60GB drive a two platter or a single (ie, how tall is it?)

Hugo