Just a guess, but may be part of the main bearing thrust plate. Cummins updated the design of those and the early ones were prone to breaking after a time. Here's what the whole bearing looks like. Might need to inspect that bearing. You can buy that one separate if you don't want to replace the full set. If they show any significant wear I'd replace them all. The thrust bearing will be on the #4 journal.
if you can find a pin with a slightly larger head and it has to be thinner than the bearing shell thickness can be used to roll the bearing half out of the block. that's how we used to do bearings in big trucks doing inframe rebuilds. put it in the oil hole and slowly turn the crankshaft.