A late comment about the rivets. These commonly have heads behind the largest sprocket that can simply be ground off with a Dremel tool (an alternative to drilling). Grind the heads off, take a small punch and start driving the rivet back through the cassette towards the small sprockets, and they usually come out just fine. If you don't have a small punch, even just a Philips screwdriver will work. Punch the end of the rivet just low enough to where you can remove the largest sprocket. That now exposes fresh rivet...drive that down until you can remove the spacer. That now exposes fresh rivet...drive that down until you can remove the next sprocket...etc. It usually takes five minutes to disassemble a cassette in this way.
Granted, some newer cassettes have flush rivet heads which make it a little less easy. And some use screws instead of rivets, which are even easier. It just depends on the cassette.