I think the main issue at play here is the kernel partition needed to be enlarged for these devices at some point (yep - commit 0dbe754e43). Best approach would be to boot into the Linksys firmware (if you still have it) and flash OpenWrt again from there, with the factory image.
Back up your settings first, and reconfigure after a clean install using the backed up configuration as your guide (do not copy them over verbatim).