We got a set of cylinder heads (advertised as 71 heads) with the engine block we purchased. After noticing the numbers didn't match i looked them up to see one is 1237661 (70-71 455) and the other is 1231786 (67-69(70)) 400/430/455). The only reason I ask is because of 2 different resources saying close to the same thing but not quite the same. https://www.teambuick.com/reference/casting_numbers_big_block.php http://www.buicks.net/shop/reference/bigblock_casting_numbers.html Thanks as always for your knowledge. Dave