Length of crankshaft/ harmonic balancer bolt?

So, I can’t find the friggin’ bolt that came out of the crank, and I went and bought the shortest, 5/8 -18 grade 8 bolt they had. Seems like it is 2 1/2 or 3 inch in length. When I tried to torque the bolt, it feels like I ran out of thread and couldn’t get the 120 lb/ft I wanted to on the crank. Just felt like it was bottoming out first. So what is the actual length supposed to be?

We have it documented here