Crate part # 3963516 denotes finished honed 4.250" bore block, with factory cast notches at bore bottoms to clear 4.00" stroke 454 crank. Counter exchange block.....3.76" stroke crank gives you a 427, 4.00" stroke crank gives you a 454. The only rarity to a 3999289 casting block, is this one being a 4 bolt main block. The majority of 289 blocks were 2 bolts.