You have block filler..it's not concrete...lol. It acts like iron, not cement. To answer you, it's put in to help stabilize either bore walls, or main webbing, or both. You have a "short fill", which is mainly main webbing. You lost a bit of your cooling system volume and surface area with that fill. So you need to build thinking that way. A biogger radiator than even the booxs say you need, and no engine with block fill should be run without an oil cooler if it's street driven. Oil works as much or more than antifreeze to cool the parts. So use a cooler (looks like a good trans cooler) and you're fine.
