Crank gear not seated.

You could always try using a wood "stake" as a punch to hammer on the crank gear. It will absorb some of the impact.

At the engine factory we used a hydraulic cylinder to press the crank gear on.

We also used a pneumatic cylinder to set the thrust bearing by hitting the crank back and forth a few times to seat the thrust bearing fore/aft by hammering it back and forth with sharp hits. It won't hurt the thrust bearing to give it a few taps - it's designed to take load.

Many of the small blocks that I've built have had a bearing that you could press on by hand, others are a little tighter.

If you don't want to use too much force to seat the crank gear, then maybe take it off and "dust" the ID with sandpaper a little to loosen up the fit, but then clean the chips off before installing to the engine...