@btmerz Actually someone already did it :)
You can find Mysensors library compatible with LGT8Fxxx here: https://github.com/KooLru/MySensors/tree/LGT8F and short description here: https://koolru.livejournal.com/134201.html? - unfortunately in Russian, so just use google translator.
I'm using this version of Mysensors library for quite a long time, building several nodes based on LGT8F328P, and it is working stable for years now. Maybe it's worth to merge it with new release of MySensors?