Not all coolers will work with both sockets. This is mainly true for older designs. The clip needed for AMD socket A was far stronger than what Socket370 designs used, so it took awhile to make them work on both types. Also some of the more exotic clip designs wouldn't work on both, like the original orb design where you twisted the heatsink on, which obviously crushed an Athlon core.
However most sites list the GC68 as being used on SocketA systems with good performance (up to 1800+ rating).
svc.com actually has all the SocketA and Socket370 heatsinks listed on one page and the description mentions the 1800+ Athlon rating.