Chevy 235 Lifter Question

I recently bought a 58-62 block Chevy 235 that hasn't run in a few years. When I pulled the side cover, I noticed that there were 3 U shaped clips just lying next to the push rods.





Supposedly, the engine ran great when it was pulled 3 years ago. What would cause the lifter to rise up so high that it would knock out 3 of the clips?

I am hesitant to so much as turn the engine over until I know what is causing this.

Thanks

 

I would, no doubt, replace the lifters with missing clips before running it.

 

Over revving? Extremely high oil pressure? Take it apart and inspect.

 

I asked someone about this and they said that this happens occasionally in engines with hydraulic lifters, and that just putting the clips back in place should be all I need.

Is there any truth to this? Either way, I will still inspect the lifters before I do anything else.