the original PS box on my 69 Coronet R/T is G2267262 and has the 1-68 as well. believe the 68 is for 1968. also has a 10-21. my thought was this was the cast date 10-21-68 since my SPD was 12-3-68. there is also a 4 digit date code up near the aluminum fitting for the low pressure hose (small numbers may be buried under gunk). mine was 3178 (317th day of 68) again SPD was 12-3-68.