1972 318, coolant getting into oil

So, I just got my Demon out of storage. On the 2 mile ride home, it overheated. It put a gallon of coolant into the engine oil. It also had coolant in the air cleaner. I pulled the plugs, no coolant on them. It also ran good,no missing, or running rough. I pressure tested the cooling system. I thought I could hear the coolant draining into the oil pan. There is no coolant in the cylinders. Pull intake, no signs of gasket failure. I thought I once heard someone saying timing covers can go bad? Any one heard of this before?