The 3 digit number will be stamped on the side that goes in the crossmember. Even last digit is right side, odd is left side. 624/625 is 1964 A body w/ 273 engine.
Side and front to back do matter if installing used bars as they have a memory.
If they are marked L & R then someone marked them. I have never seen them marked from the factory except for the last 3 digits of the part number.