Hello gents!
I have this AR7 router for long time, and would like some extra apps on it.
There's actually great OS firmware created specifically for this device - OpenWAG200 - http://openwag200.sourceforge.net/ .
But it's features are limited and it is not expandable - I need ptppd, for example.
I did a google and OpenWRT forum search, and indeed found some people trying to put OpenWRT on this device - never with followup, never with concrete instructions on how to do it.
This is AR7 device, and here are some links you may find useful:
https://dev.openwrt.org/ticket/5298 - ticket in the dev system for supporting this device. Dead for some time already, sadly... 
http://oldwiki.openwrt.org/OpenWrtDocs(2f)Hardware(2f)Linksys(2f)WAG200.html - hardware info from openwrt wiki.
http://wiki.openwrt.org/oldwiki/OpenWrtDocs/Hardware/AddonTech/ARM8100 - probably closest (supported) device to WAG200G you can find.
http://openwag200.sourceforge.net/?p=hardware - even more hadware info (OpenWAG200)
http://openwag200.sourceforge.net/?p=runningsoftwareinqemu - OpenWAG200 in qemu (bootlog included).
The main sticking point seems to be the .IMG firmware format, instead of OpenWRT .BIN. OpenWAG200 has source code and instructions on how to build it - http://openwag200.sourceforge.net/?p=rebuild . Perhaps it will be helpful.
I'd really love to put OpenWRT on it, and it seems like it isn't far away! Waiting for any comments.
Best regards, sonya. 