Blowing out freeze out plug after start up

Could not afford bring it back to the machine shop. Decided to go for it and replace the head gaskets. During that time I bought a bunch of rubber plugs and plugged off the block and blew the block out with compressed air. The air flow seemed to get much better like it blew something out. Did the same with the heads. Reassembled everything, no freeze out plugs blowing out, no, overheating. I was/ am ecstatic. Dialed everything else in, engine runs great. I feel it was something restricting the block coolant flow or the heads. Lesson
learned, when things look real bad and expensive, take a chance......