You can do this without an issue, as long as you can use VLANs on all the gear that make up your network data flow to both sites. Meaning the router that handles the communications can do vlanning. Your best be in this scenario, is your 8600s handle your WAN ips.
From there you have to setup is vlan tagging across your wan link. This will allow you use the same subnet (Vlan) at both locations.
If you have a firewall or router between these two sites that do not handle vlan tagging, then this will not work for you. You will not be able to split the same subnet across the two sites. (Not that I know of...)
8600s
470---8600---(tagged packets)---8600---470
If you need more info on how to set this up, please let me know. I will shoot you more specifics.