I have based freecad on the commit for the release tag for version 0.18.2 (0.18.3 was released after my patches were submitted). I looked at the commit for 0.18.3 and I don't see why I couldn't use that one. I just need to find the time to do the work. As for a working version you can see my prior work in the channel at
https://github.com/jsoo1/guix-channel on commit 9fd2815ed08317d27e174ca460e0d0a2be058aa7.