External or Internal Flywheel… need asst.

Max1196 said

NO, that is not necessarily a neutral balanced flywheel. The clocking of those two holes at the 8 o'clock position in your picture could still indicate a 340 cast set up. Go to post #2, then proceed.

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That's exactly what I was thinking, hence my suggestion to check the damper. The flywheel counterbalancing on a cast-crank 340 is a hell of a lot less than it is on a 360, so it's less obvious. Fun fact: A 340 cast crank is "zero balance" when used in a 318.

@madhatta360: If it turns out to be an aftermarket damper, look for a counterweight bolted in from the rear (timing cover side), in the area of the pulley bolt holes. The counterweight should be stamped with its application.

It's probably worth mentioning (as it has been many times) don't sweat having a cast crank. You aren't going to hurt it unless you plan a 500 shot of nitrous at 7 grand on 35° of timing. Even then, the block will probably let go first.