[CentOS] Howto install Centos6/7 Comcast WA/OR

Has anyone managed to install a Centos6 or Centos7 in Washington or 
Orgegon, or anywhere else that Comcast has deployed the IPV6to4 
routers.  The router in question is a Xfinity DCP3939 Router with 
Wireless, and I'm trying to get a Centos system working behind that 
router (with a wired connection), and enable SSH access from outside.

Does one have to enable both IPV6 and IPV4?
Can I enable IPV6 after install, or do I have to restart the 
installation from scratch (it has Centos6 installed via an earlier 
IPV4 router).

How does one configure the router so that its DHCP system awards a 
known address to that machine, and how to forward port 22?

The extra problem is that I'm trying to advise the owner of this 
configuration remotely.  Behind that same router he has a working 
Windows 7 machine, and I can use Team Viewer to view the router's 
configuration from "inside".

Any assistance would be appreciated.  Comcast is of no help.

David