After the engine overheated, I found some weird gunk in my radiator

I got stuck in traffic driving my 1972 Coronet in the city today, the temp gauge never went over 3/4 of the way, but when I parked and turned off the car, steam billowed out and a bit of coolant spilled too. After letting it cool down I opened the radiator cap to put in some distilled water, but I saw two pieces of some weird gunky substance. I managed to fish them out, I have no idea if there is any more in there that I can't see. I'm just here to ask if this is normal or something I should worry about. I really NEED the car first thing tomorrow for work...

I do not remember what coolant was in the engine, which is a somewhat recently rebuilt 318.
Author: admin