If the 46 is running the original cooling system, it's a "zero-pressure" system. As long as the cracked area of the block is cleaned thoroughly, a coat of "Marine Tex" over the crack and an inch or so beyond it in all directions, it should contain any leaks. If you press a piece of 40 grit sandpaper over the repair as it's curing, the texture of the patch will be almost exactly like the surrounding cast iron.
Jerry
