The Alpha PEP-66 was the top of the line
HSF roughly two and a half years ago. It was the most expensive
HSF available at the time and was designed specifically for use on Slockets.
I'm giving my brother my P3B-F Slot 1 P3E 600 machine for Christmas. As my PEP-66 is the only Slocket
HSF I have, I want to get rid of, ahem, I want him to have it for the Slocketed P3E. Perhaps the wimpy wire clip for the PEP-66 got stretched a bit when I tried it on a S370 mainboard. Maybe a S370 Celly has a different "geometry" than a FC-PGA CPU and this "tired out" the wire clip.
I ordered a stronger Version 2 wire clip for the Alpha from 2cooltek. This new clip is a good deal wider and getting it between the fins of the HS distorts it a lot. It needs forcing, and by the time it reaches the point where it will engage the lugs of the S370 it's bent far out of true. It required fiddling with so that no light could be seen through the top of the CPU/bottom of the HS junction. The upshot is that a GW FOP-38 works a little better, using an identical Delta screamer.
Maybe the crux of the biscuit is that a new $5 clip does not a new heatsink make!