I've only had 1 magnum engine in my life but from what I've read and heard about them is that they are a thin wall casting and a 0.030 over bore is the limit is this true? Also I've heard that the magnum blocks are known for cracking. My experience has been with blocks from the 60's and 70's and they could take a 0.060" over bore. Also are the magnum blocks a 1 piece rear main seal block, would a magnum block be a better choice over a LA block? I'm looking for more longevity and mild performance build. Also what would be a good compression ratio for a 300-325 horsepower at the flywheel? Again I don't have any knowledge about the magnum blocks just what I've read and what I've heard. I thought that it be best to ask you guys that deal with engine's daily. I really like the a body site. Thanks for everybody's help and sharing of their experiences and knowledge.