Ah, ye of little faith. Wikiloc to the rescue. Take a look at these tracks.
The author has a lot of pictures and a huge narrative explaining the walk. I have only skimmed it, but he describes how he put this route together and then describes it. It joins the Inivierno, I think, in Salcedo, which is a little before Pobra de Brollón, so you would actually be on the Invierno a stage before Monforte. It’s all in Spanish but google will translate.
One other thing I would say about Wikiloc tracks is that you should feel free to ask a question — there is a “comment box” down at the very end of the photo stream. I routinely ask people questions about their tracks and have to say I have never been disappointed.
I can’t vouch for this route, but everything I see looks promising.