69 383 Water Pump Housing Casting Defect?

The engine did have stop leak put in it to fix an exhaust bolt leak on the passenger side. I am now pretty confident that the problem is a blockage issue now though. I have never seen this much junk in the radiator before, I would guess the new pump stirred a lot of crap up. There’s a whole mountain of sand in the radiator, and I took the radiator out and reverse flushed it three or four days ago, so this is all from just a few miles of driving. IMG_1292.jpegIMG_1293.jpeg