sounds like you got leaks all over---could be wrong head gasket for 400 block and also the 400 blocks crack pretty bad from the steam holes to the bolt holes to the cylinder---400s have 2 small steam holes between the cylinders to feed water from the block to the head---if you have the wrong gaskets or the wrong heads can be a problem---also these blocks are syameez bores and they crack from those steam holes to the bolt holes to the cylinder---cracks may not show up until the bolts are torqued