90 degree 340 adaptor

adding a 340 90 degree adaptor to my small block, the large center bolt came with a cork seal/washer and a small thin fiber washer, as well has the large gasket to the block, in any ones opinion , which seals/works better for sealing control the fiber or the cork? don't want dripping oil on my headers, or do away and use copper crush washer gaskets?
installing this weekend, looking for some heads up information, would be awesome.. thanks...