Take them heads to a shop that does heads, get them cleaned up and magna flux tested for cracks. I believe, if it were Mine engine, I would send them injectors over to Blue Ox and have him test them, and, balance them while He is at it. I have never seen brass like that caused from any kind of a stop leak substance. I`m thinking that someone created their own kind of a stop leak and dumped in plenty of the crap. I am also guessing that the reason they did that, and the new water/coolant pump, is because it could possibly been having cooling system issues.