Use AD Groups Instead of Linux Groups

On our file server, we are using a bunch of Linux groups that are still in use and need to be replaced by their counterparts in AD. The groups in AD and /etc/groups have an identical name, so, (I'm guessing?) chgrp won't really be of much use here. My question is this: What's the best way of changing the group ownership of specific files on our file server to point to the groups in AD instead of the Linux groups? I was thinking of possibly changing by GID instead of group names, but that just seems like a recipe for disaster.