CybervisionPPC cooling for Permedia 2

[my_pc_is_amiga]

I've had a copper heat sink attached with some double side thermal tape.  I'm trying to figure out if there might be a better fan/heat sink solution that could use the 4 holes around the permedia 2 to clip on a fan/heat sink combo for better cooling. 

What size fan/heat sink fits on the permedia 2 and does anybody know a part number/brand that works?

Thanks in advance for any suggestions.

[my_pc_is_amiga]

Thanks a lot for the advice.  I ended getting a 24mm fan and got the head of the screws attached on top of the heat sink with some epoxy.  Attaching a pic.