There is a post in the Comcast HSI section of the Forum.
To get it working with the delayed WAN connect, I did the following:
1) Changed IPv6 settings to WAN DHCP, LAN Auto Config, Secured.
2) Unplug modem and router.
3) Unplug WAN cable (yellow plug) on the router.
4) Wait 2 minutes.
5) Plug in modem.
6) Wait 2 minutes. Modem startup lights should be solid or otherwise indicate successful startup.
7) Plug in router.
8) WNDR3700v1 power light will come on immediately as AMBER.
9) Wait 2 minutes. Router should be finished starting up and power light should be GREEN.
10) Plug in WAN cable to router.
After doing this, I got an IPv6 address on both WAN and LAN, and all IPv6 tests that I could find passed.