I've seen small pieces get embedded in aluminum heads before,some have spit debris out and ran like nothing happened,it is amazing. I guess kinda lucky also,that a valve isn't bent or a cracked piston...I lost a valve keeper in a 283 years ago,did the same,cleaned and smoothed out,it didn't affect the engine at all when I was done,completely different engine though.Maybe you'll have the same result. I wonder if it will ping after you get it back together? Hope it works out good,can't wait to see the pics