Cylinders, pistons, and cranks on the D&B..I saw the prototypes at Toledo many years ago...Since the cylinders on the Echo twin chainsaw are different, they buy the same side cylinders to get the spark plugs the same on both sides..
BME uses the whole engine on the smaller single, probably only the cylinder and pistons on the other sizes....You could call Keith and ask
Any Echo can be converted, some just work better than others....