where do you find the casting date for the heads and the block, as far as the day and year. Ive got a 396021 F Block with E heads on it. A guy in florida told me that this combo and the 1970 manufacture date is the best 455 year they made. I dont know alot yet about these motors but am looking for a calabaration of this or some other comments. Trying to build a streetable engine..