This has probably been answered like a thousand times...

Welcome aboard! You can find the engine year and size stamped into the top of the block over by the coil mounting. If your engine is original, it should say A17, A170, A22, or A225. Other years will have different letter codes but the number will indicate the size. 17 is a 170, 19 is a 198, 22 is a 225. The letter codes are R (1961) S (1962) T (1963) V (1964) then they started over with A (1965) B (1966) and so forth up to 1973 when they went to a number code that indicated the year.