The epoxy Intel used on the OverDrive line of CPU's is among the toughest I have ever encountered. That goes from the 486's through the Pentium line. Normally I would suggest a heat gun or solder reflow gun, but that type of thermal epoxy is so tough it doesn't help that much. If you live in an area that you can still get some freon then I suggest that. Yeah, the cold temps help make the epoxy brittle, but the freon will also breakdown many types of epoxy (like a low grade acid), and won't hurt the chip. However, getting freon nowadays is both hard and expensive so that's probably not an option. If you do manage it, make sure you do the work outside to avoid the toxic fumes that will build up in a normally ventilated room.
I really can't think of to many options when it comes to the OverDrive chips as they are a real pain in the butt with that super epoxy Intel used. One or two of OD chips had a heatsink that was built into the chip package and couldn't be removed, but yours is not one of those. It can be removed, but it's going to take time, effort, and patience. Careful use of a thin bread knife can provide uniform pressure when trying to separate the heatsink from the package. Thin razors are a danger and a pain with normal epoxy, but almost useless with the Intel stuff. I would just recommend many trips to the freezer and carefully prying with the bread knife. As soon as the chips starts to feel warmer in your hands, stick it back in the freezer for an hour and try again. Might take a few days of doing it that way, but it will work.
You'll have to man handle it a bit, but pay attention and you shouldn't do any damage. When the heatsink finally pops off, then hopefully most of the epoxy will be on the heatsink and not the chip package. If you still have a large amount on the package, you will have to carefully remove it with a fresh razor while not scratching the surface of the package. Again, patience is key. Good luck.