That hole belongs there. You weld it closed and your cam/distributor gear will burn up. That hole channels some of the oil from the lifter valley over the cam/dizzy gears, along with the front oil return holes from the heads. It helps keep them cool. If it looks broken it's because nothing needs to move through it, it's non machined, and as a result has very rough casting, sometimes rough enough to cut your finger on.

 

Is that soemthing that could (or should) be cleaned up with a die grinder? I plan on removing all the flash from the block anyway.

 

Couldn't hurt cleaning it up a bit I suppose.

 

Yeah, nothing wrong with cleaning it up if you want to. Not necessary though. If you do, just make sure you clean the block really well, you don't want crud getting into the lifter galleries because it could jam up your lifters.