I have flywheels from a '68 240 engine and an '80 300 engine, plus a 300 flywheel of unknown year. None of these has a cast-in weight. I understand that some engines are externally balanced, but I thought that these were all V-8's. I would really like to know if any of the 240/300 I-6's were externally balanced and, if possible why. With longer and longer strokes, the V-8's did not have room in the crankcase, hence the need for the "Detroit" balance. Will a 302-series flywheel bolt up to a 240/300 crank? If so, that could be the problem.