Your first clue will be in casting numbers on various parts of the engine. C = 1960's and the next digit will be a number representing the year the part was cast, e.g. C8OE would be 1968. This is not definite beacuse many of the parts are interchangeable, but if you have alot of C6 numbers, then it probably is a 66 289. They started making 302's in 1968. You can find a casting number for the block behind the starter.