I was the ddwrt forum member who figured out how to get the WHR-1166D to look for an image via TFTP and posted the details back in 2015. Because I didn't ever figure out how to build an initramfs image that would work, I hoped that someone would pick up the baton and run with it.
I found this page a couple days ago and finally got rid of the Buffalo firmware and installed OpenWrt last night.
Thanks for your effort in contributing a build that got me to 18.06.2.