1966 slant six 170 timing mark

Hey guys. Checking the timing on the slant six but I don't see a timing mark. Harmonic balancer could be too cruddy to see it without sanding around it. But is this half moon part of the timing mark? I'm used to seeing a little slit on the harmonic balancer. I have the distributor pointed to #1 cylinder where the harmonic balancer is. Also should I have a bolt holding the harmonic balancer on?

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