Finally got it back together. It was definitely a head gasket although the original cause was corrosion of the head that got into the cylinder sealing ring. I had to have the heads planed to get a decent sealing surface back. I also saw that the original intake gaskets were sucking oil. The intake ports were full of sludge. The tops of the pistons had a thick layer of carbon. Cleaned that all off. By the way, there is only one option for a head gasket set for this generation 3400 and it includes the good intake gaskets. The car runs very well now.
I also have a 1998 Monte with a 3100 with about the same number of miles. I think I'm going to replace the head gaskets just as preventative maintenance. Thanks everyone for your replies.