Mt Whitney Zone Forums General Discussion Equipment for belay on Willamson chimney?

There is more than one class 3 route on Williamson. Which one are you considering? Is it this one:
https://www.summitpost.org/west-face/156690
https://www.youtube.com/watch?v=YRU1ir5pcWs

You say "belay from top". Top of the route or top of the peak???

You ought to be prepared for whatever you find, especially if you are not familiar with Mt. Williamson and have people with you who might want a belay, and might want to reppel off the peak.

If you decide to setup a belay using slings, beware of loose rocks.