Jani,

Actually, 1961 was the last year of 283 in the Vette. From '62 to early '65 only 327, then 396 was added in '65.

Based on the number you posted, the engine is F= Flint plant, 03=March, 15=15th day, WA=283. My source indicates the WA is 1965, but since it didn't have any later date decode that could mean WA was used 1965 thru 1967.