slant six help needed, burning oil

Valve guide seals. *rart rart* Intake manifold might run into oil on the slant, what gasket did you use? 63'-74' you need to remove the washer on the spark plugs or they won't seat deep enough.

http://www.allpar.com/fix/spark-plug-tubes.html

Heat cycles do weird stuff to mating surfaces. Double check the snug on it.