The outside dimensions of the socket itself(but not the pinouts in the center of the sockets) are the same for Socket 7, Socket A and Socket 370.
As Socket 7 is nearly history, we can leave it out of the discussion from here on.
What makes the real difference between Socket A and Socket 370, as far as the heatsinks are concerned are the processors themselves. Durons and Thunderbirds have factory applied pads near their four corners. CII's and P3E's have no pads.
A flat bottomed heatsink(leaving the "shelf" on the bottom of the HS that accommodates the edge of the socket that has the cam box in it for the lever out of the picture) mates perfectly with Durons and T-Birds. At least in theory. Some HS's mate perfectly with un-"padded" P3E's and CII's, as well as Durons/T-Birds. This is something you have to eyeball carefully!
Some Alpha HS's come with rubber feet. Older ones all had nylon feet that had to be removed for T-Bird use. Nowadays, Alpha's come with no feet. They're AMD ready, however stick-on feet are supplied for use with Intel CPU's.
Then there are shims. Durons and T-Birds are more fragile than CII/PIII's. Some folks think that shims are necessary to protect the fragile glass slugs of AMD CPU's. Some people think copper shims aid in optimal HS mounting on P3/CII's.
There are electrically non-conductive as well as copper shims. Non-conductive ones are probably smart for T-Birds and Durons! All those tiny bridges on top of the processors seem to make copper a dangerous choice.
Hope this helps.
shims are a wonderfull things, besides keeping you from cracking the core they also ensure your hsf are sitting level with the socket. Get a nonconductive shim however, copper shims can produce much HIGHER temps than a non conductive shim or a cpu without a shim.