Hello I want to replace the pan gasket on my 383 to a one piece rubber. I do not know if I have the thick or thin front seal . Casting numbers are 3970010 . What year it is , I have no clue . 69-late 70's is what I came up with . Also what kind of core should I get , metal ? Thanks

It's not the casting number of the block that matters, it's the part number of the pan. Older pans use the thin seal and less-old ones use the thick seal. Measure the distance block mating surface to the lowest point of the lip on the front of the pan. If it's 2 3/8", use the thick seal. If it's 2 1/4", use the thin one.

Thank you . I have a new aftermarket 5 quart pan with no part #s on it . I assume it has the newer thick gasket .

you will want to use the thick one....use one for a 77-81 camaro.they are the same............i used the thick one with no problems and never had any leaks...btw the one peice oil pan gasket has metal inserts so it cannot get crushed..........i like them because they are re useable.

Thanks for all the info

Just to add a little more to the above info, probably about 99.9% of all aftermarket SBC oil pans are set up for the thick gasket. The last time I can recall using the thin seal was years ago on a motor with an ancient relic of a factory pan on it. Lol.