I have a compaq with cel 300 with a passive heatsink.(just slightly larger than normal, slightly)
It was positioned near the power supply air entry so that it could take advantage of the moving air.
Always has worked great, I use it for a test machine. That way I don't mess up my workstations or server.
My P2 333 was set up rather odd... only had a large heatsink... very large...
and you could connect a fan to its side if you wanted , but i did test it and it did run fine without the fan.... although i never tried it overclocked without FANS on it as it did run hot @ 333 without