The 76-78 blocks are the same casting outside, they do have larger water jackets, which is why you can only bore them to a .030 max to be safe. The motor home block is the same as all the blocks cast from 76-78. The machine is what makes them a motor home block. As mentioned earlier, there are 2 small holes drilled per cylinder in the deck to the water jackets, lined up with the spark plus and between the head bolts. The heads will have the same holes. These blocks are as good as any early block.