I think that's a parts gun. Appears to be a 52-1 frame, and one that has been to Europe as it has proofmarks.
Top end is not from the same time period, it appears to be a 39-2 with the more modern style extractor. It is also wearing a 39-2 fully adjustable rear sight which was inly available as an accessory, and not shipped that way originally. The top end was made some time after 1970.
The 52-1 frame looks mostly correct, but the original hammer has been swapped out for a 39 hammer. That was a curious decision by whoever altered this pistol as it surely is not an upgrade from the original hammer that came on that frame.
I would guess the magazine is a sloppy fit in the frame.
It is an interesting setup and could be quite enjoyable as a shooter, but I don't believe it is worth a premium and I also believe that a factory letter would indicate that the frame left the factory in the late 1960's as a 5-inch .38 Wadcutter gun and not the configuration we see here.
