Used gears will 9 times out of 10 howl and whine. Think about it. They were setup in the differential and adjusted originally. (backlash, pre-load, etc..) Now you pull them out and swap them into your diff and try to set them to spec. Problem is they have however many miles on them and they will wear. So the chances are they will work yes, but they may make noise since they wore originally setup in a different diff.
Gears are cheap enough buy them new. Now if you can find an SC diff with gears in it used and swap the whole entire differential over that is fine. But when you install used gears in your car, don't expect them to be perfect.
A guy I work with has been setting up rear ends for many years. I think I'm going to have him do mine when I buy new gears. I was asking him about gears and stuff and I said what about used gears. His exact words were "are you ~~~~in' crazy?" then he proceeded to explain about the whine and growl and stuff because of how the gears will wear. I take his word for it, I mean he has only been doing this for a living for the past 25 years.