I am a little late to the party but after reading this thread I had to dig out my old pre-40 shipped in May, 1956. Mine has the screw at the top of the frame, flat latch and lock down pin. However, the finish is bright and I can only find the sn 761X on the butt. The flat on the barrel is blank as is the back of the cylinder. Ejector star does not appear to have any markings either. Trigger has been replaced at some point as it is thin, smooth and non-case hardened. This revolver belonged to a good friend who got me into the shooting sports but passed away a few years ago. It’s a keeper.