The Rampant Lion is the symbol of the Brescia proof house, though this gun seems to predate National proof rules of Italy in 1923. I find the shaping of the hammers and action very similar to Italian guns of mine. The fences are more elegantly shaped that any other that I have seen, as is the breech reinforcement.
I think the SA mark on the action flats is likely the makers mark.
A lovely find indeed, and an intriguing mystery.