Just saw your other post and see it's in the stang. The 20 you see under the oil filter is part of the date code. There should be more and you might have to wire brush the area a little to see it all clearly. Your looking for a number/letter/number(s) sequence. Also the heads have a casting number and date code. The heads casting number is between the center two spark plugs and the date code above it under the valve cover. Almost everything on the engine will have some sort date code or casting/part number. Now I'm not sure if you can find out the build date of your car or not but without it you can only estimate by the date codes if they are correct. With the build date you can determine if they are original to the car. Kevin Marti would be the one to contact. I know 68 and later info is there but not sure on 67. Perhaps someone else can clue you in on that also. G.