It has the 3rd and last style flat latch. Flat latches were not used after 1966.
1959 production that likely shipped last quarter of 1959.
THREE STYLES OF FLAT LATCHES:
1st style flat latch used only on the Baby J frame and K frame airweights:
Photo by jackvs1
2nd style flat latch began on the Improved I frames, K frame airweights, and Baby Js just prior to the Model of 1953 New J frames shown here:
3rd style shown on lower .38 Chief Spl. in first photo, with steeper incline at the front, and in 2nd photo; also used on Model of 1953 New I and New J frames, and K frame Airweights beginning mid late ‘50s; ending in 1966.