Do you have "Sotilaskäsiaseet Suomessa / Military Small Arms in Finland" book series by Palokangas? Part 2 pages 172 - 173 contain some photos of two rifle M/35 prototypes.I am impressed with how good the small M39 looks from a distance in the pictures. If not a bubba job, might it be a possible experimental model, perhaps an updated later experimental version of the mysterious M35 Finn SA short rifle often mentioned but never pictured?
The 7.62 mm x 39 prototypes were called M/91-56 and M/39-56.Doug Bowser, in aka SA man's "Rifles of the Snow" and Rifles of the White Death" has mention and sketches of various experimental models based on M27s and M39s. Is the caliber standard 7.62 x 53 R or 54 R, or is it 7.62 X 39 MM, as the Finns were supposed to have been experimenting with short carbine sized M39s based rifles in that Russian short ammo, etc.
Nice buy, I would have bought it too, even if just for the novelty!