I'm considering using an 80 mm fan with an airflow of 19 cfm on a 60 to 80 mm fan adapter to cool my K6-2 500 Mhz CPU.

Will this work?

It's a Swiftkill adapter, by Innovatek. Stupid name, but there you go.

thanks in advance

Any takers?

Does anyone have experience with 60 to 80 mm adapters?

I gather they don't provide better cooling, but they might fit quieter fans.

Yes, that's about the gist of it. They do allow quieter fans to be used, and sometimes, cooling can be slightly improved, but not much, and probably not if you're going to make it run significantly quieter.