Yeah I am hoping that is not the case. It did sit for a while, but was in a garage. It does have antifreeze in it so I would hope it didnt crack but who knows. I am going to try pressurizing the cooling system like suggested.

There isn't any way the valve being stuck open could have let coolant somehow back into the intake manifold when I was cranking the motor over? Ive never worked on a flathead motor so not 100% sure whats going on under the head.