We have a dual chassis core with single sup 720-3B's. I am planning on upgrading them to dual sup 720-10G-3C's without VSS for the time being. So the question is can I do a zero downtime upgrade by installing the 3C sup in with the existing 3B and create a working failover scenario. At which point I would pull the 3B and add the second 3C effectively causing no downtime. Thoughts on this would be greatly appreciated. Thanks.