Rick, I have the same problem with the '79 300SD. I guess it is a quirk of these 617.950 engines.
My theory is that it is the "test tube effect". When reading liquid level in a test tube you use the middle of the bubble not the higher edges. As liquid finds it's own level it would be more logical that the high reading is wrong. Perhaps the high side is against the edge of the oil pan or nearer to an object causing a higher area. It is very difficult for a body of liquid to have a "low" recessed area. I would go by the lower mark as the true level.