72 455 popping at carb and clunk

Sorry forgot to add those

 

Wire wheel the pistons (top) if your reusing them

 

Hey guys I've stripped the block down and preparing to do the oil mods before taking engine to the machine shop. I have a quick question , is the center holes on the block supposed to be filled, on one side it is and the other side isn't. I've included pics of both sides or is this something that should be open so I need to drill it out. If it is suppose to be open was this done in the casting stage?

 

What's the purpose of this area of the engine block?

 

That's where the pistons go

 

I guess I wasn't specific enough lol, i have arrows pointing to the holes that I meant, is that just rust that' formed in the block?

 

Yep, that's just goop