Bob,
You do indeed have a very nice Pre model 36 being a Model of 1953 with all of its J frame improvements with 2nd or 3rd style flat latch. It has a 3 screw sideplate which dates it to between c.1955 to 1957 and a serial # dating to 1957. It's right on the cusp of having Mod 36 stamped (which happened c. 1957) in the yoke (crane is Colt's term).
It probably only has the serial # in three of the original 6 locations; butt, under ejector star and backside of right grip.
This photo will help you determine which flat latch you have, 2nd style on left or 3rd and last style on the right:
