No. It's a tall deck/long rod version of the Cleveland small block, with the same bore center distance and head bolt pattern as the Windsor small blocks. It's deck height is 10.297" vs 9.206" C and 9.480"/9.503" W. It has 3" main bearings like the W, bigger than the 2.75" for the C. Bearing surface speed is an issue if you're running high rpm with the bigger mains. The M shares bell housing pattern with the 429/460, and has unique engine mounts. It's as tall and wide as a big block, but the same length as a small block.