And we have a winner
Not yet, but almost.
I found out that garment which has been butchered is likely to be old Swedish army dispatch rider's motorcycle trousers
(or probably two pairs of them) like these:
I found out about it through this discussion:
hi, I can clarify for you. so what this is someone took a pair of pants issued to the MC-Ordonnans (swedish dispatch riders) in the 1950's and turned them into a jacket. on the sourced picture above that pocket on the forearm is where it is on the knee. people did these for the leather and gray cotton variants with nonremovable sherling liners for..fun I guess? the buttons are for leather suspenders. as for a maker? well, there was Oljon, Ö.S.B Örebro militärt utrustningar, Mats Larsson or Öje skinnbeklänad, but they all shared the same wool blanket liner so I can't say.
I could still try to find someone from Sweden who can confirm it, because another point of view was that it would have been some sort of experimental model, but I dont think that it is correct at least in this case.
I have owned a Swedish army motorcycle jacket and a several livpäls sheepskin coats and indeed my the first thought about this jacket was that it has something the same. For example, just the buttons. But then I didn't find any Swedish similar jacket, so I wasn't sure anymore...