I had a little journey with this router and this thread was incredibly helpful, so I want to give something back. I purchased a D-Link Refurbished DIR-601/RE from Amazon for $12.99 (with Prime) with the intent to use it in client mode. It is this router, with the B1 hardware version. I looked for a dd-wrt image to use, but didn't find one. I did thankfully get pointed here.
Long story short, most of the links to images were broken by the time I got here. The only one that worked was the very first one from jay0lee, and that build didn't have luci and was a little low on space to work with. I bit the bullet and built my own image from source. It's actually not too bad. As jay0lee says, credit to the OpenWRT devs.
Here's a link for my builds that hopefully keeps working: https://drive.google.com/folderview?id= … p=sharing. The folder includes all three images that my build spit out. Not sure what the exact difference between the normal and the -NA image is, but you can try them both. I used the sysupgrade image because I already had jay0lee's build installed. I haven't tried the other two, but please do and let me know what happens.
I cut as much as I could out of the build to keep the size down. The only thing that might matter to someone is that I cut PPP (and thus PPPoE). I built with the micro c-lib rather than the standard one, and I think that makes opkg unhappy when trying to install things. Hopefully the build has everything you need though.
After installing, I tried the various methods to setup something like client mode. This is the one that worked for me: http://wiki.openwrt.org/doc/recipes/relayclient. The build does include relayd.
Thanks everyone who has contributed to this thread. Hopefully this helps some wayward internet soul.