CAT guys...

Got some end shots? Ive never redone the inside of the engine personally, but w.a.g. is its the end of a therm probe

 

Its the thing-a-ma-jigger that allows the dodad to connect to the whirlygig which allows the thingamabob to do the whatchacall it with the dohickey.

In all seriousness i think skall is correct. Looks like a probe end to me.

 

Looks the pin from chain, or a keeper from somewhere.

@wore out

 

Looks like the pin from the Jake Brake that rides in the injector arm.

 

see page 5 and 8 Master Piston Assembly

 

Its a risk, given that your jakes are now not properly functioning and you have at minimum a few washers and a spring still floating around in there. you need to pull the valve covers at minimum to assess what the damage is or isnt.

Is that a death sentence and you need to tow it NOW, no, but it isnt wise to run it more than strictly speaking neccessary either. With any luck, all bits and peices fell into the oil pan damaging nothing on the way and the oil pickup strainer will keep them from causing further damage.

I would definitely avoid using the jake if at all possible till you got it checked though

 

Its a ticking time bomb. Might run forever, might make it 5 minutes. Might be leftover from a repair from before you owned it. If the jake's working fine and what not I'd say the last scenario is most likely. I still would investigate before I put the truck back in service. A couple hours of downtime to pull the valve covers and check things over beats being down a few weeks with an engine failure.