there are casting dates on various parts of a CS. on the crank case there should be a number, single letter from A to L, then a two digit number. the first number is the day of the month, the letter is the month (A=Jan, B=Feb, L=Dec), the last two digits is the year. mine is 3L53. there is also a casting mark on the inside of one of the spokes on the flywheel. again mine is 8L53. this is just a rough dating as the engine was assembled in early 1954.
you have to thank Ken Boak for this.