It depends whether you'll have a Socket A, or Slot A mainboard. The Alpha PAL35t(why mess around? Get it with the 38 cfm Delta "Black label" 60 mm fan. If a loud HSF bugs you, the YSTech "27" cfm fan's a better idea) is designed for a Socket A mainboard.
The Alpha PEP66 is designed to hang on a Slocket. The same fannage options apply. AFAIK, no Socket A mobo's are obtainable yet. A Duron in AMD Slot A form factor may require a different HSF than a Socket A CPU OR a Slocket A CPU! I don't know. In "Intel speak," the choice is simple: PAL35t for a Socket 370, PEP66 for a Slocket.
I suggest not buying the HSF until you have the new motherboard in hand. I didn't, so now I have the PAL35t AND a PEP66. Lucky me!