M30 is actually an ISM base engine
103-10. It is one of the most widely used small engines in the world, in all kinds of agricultural equipment
applications, boats and just about anything else you can think of. The engine does not have replaceable liners, they are cast integrally into the block. While it might be possible to have a machine shop bore and resleeve the block, it will be much cheaper to find a used engine from somewhere and switch your marinizing components to it. Being in Ft. Lauderdale, I'd look around the lawn service
supply places, the engines are common in lawn machinery. Also try craigs list and e bay.