The Centennial was introduced in 1952 and the front screw dropped years later so a very early example may have it. It does have the flat latch (cylinder release). I think this was changed around 1964 or so.
If it's model marked on the frame under the cylinder crane it will say M40 (steel) or M42 (alloy). If not model marked then it was made before 1957.
These are popular but this gun looks to be in pretty sorry condition as far as finish. Would still be a good carry gun (I have one that looks even worse and I like to pack because I figure I can't hurt it any more) but $600 would get a like new example. This one MIGHT bring $250 or so from someone who wanted a carry gun and didn't care about appearances.
This is my beat up carry piece with the stag grips I got for $6. Below it is a near pristine example that I can't bring myself to carry.
