I gave a talk. I believe Saami loanwords supply fair evidence that the syncretism seen in the Old Norse feminine u-stems with plurals from monosyllabic stems (<*handuR-*hendiR, *kinnuR-*kinniR) was matched by former fem. monosyllabic stems taking u-stem singular endings:
http://dx.doi.org/10.13140/RG.2.2.24439.02723/1