I have a couple saws with shredded pistons and jugs, but the cost of a new engine seems to be 3/4 the cost of a new saw. If I can get an engine from a different model, how likely am i to have a match? It seems like you can put a 55 cylinder on a 51, could I throw a 61 engine on a 51 crankcase? Could I do it if i changed the carb? Is it just a matter of the gaskets and seals lining up, or is there more to it? Thanks, saw gurus!