Actually, the engine is a very early 1965 unit. The "A" in "A383" means it was built for the 1965 model year. But the "8 18" (there is no "1965" year stamped as part of the engine number) is the date of assembly - August 18, 1964, not 1965. The complete engine number is "A383 8 18 R". The R back in 1965 meant the engine had .001" undersize crank journals.
Production of 1965 cars began in August, 1964, while the last of the 1964 models were built in late July, 1964. 1965 model year production of cars ended around the end of July, 1965.
Production of 1965 engines, though, would have begun prior to the beginning of 1965 model year production. So, "8 18" is early 1965 model year, not late.