Truck Repair: cummins 903, coolant additive, head gasket

Question
i have a 1974 cummins v903 and am getting water in the oil is there an weak spots i should check and how should they be ckecked

Answer
Man thats a dinasaur!Unfortunataly I have not had to work on one of those,but have the smaller V8's.Usually if coolant is getting in the oil & not oil in the coolant it is a bad liner,head gasket or head.Usually a liner from lack of coolant additive & liner pits from electrolisis.You could drain oil & remove pan.Pressurize cooling system & see where it comes from.