This (above) does work with dsf-python 3.5.1rc1 (as announced in https://forum.duet3d.com/post/338777).
However, I've got a slightly refined set of installation instructions for the pre-requisites:
To install dsf-python it's not necessary to download the source etc. you can just sudo pip3 install --break-system-packages --pre dsf-python (and this is better). It will moan about how you should be using a virtual environment instead, but should work. I haven't done any testing with virtual environments. (pip is deprecated, but setup.py is even more deprecated.)
For hx711py it's not set up to use pip, but if you use sudo python3 setup.py install --record files.txt it will at least write the files it installs into files.txt, which will help if you want to uninstall it in future.
Otherwise, same instructions as above.