My 305 has developed a dull bottom end knock. It is most noticable when the engine is just above idle speed. Oil pressure seems to be lower now as well (125PSI). I am guessing the bearings need replacing. Is this a big job, and can it be done without pulling the engine? The truck has 245000 km on it, and doesn't use any oil, so I am willing to fix this engine up, rather than replace the engine.