The dowel is locate the oil pipe so the oil holes line up Make sure it is not in to deep as it can block the oilway I had a crankcase altered to take the block driven oil pump On rebuilding engine did not check under the pump It smoked and used all the oil nearly wrecking the motor Stripping it back down no balls or spring and the gasket damaged allowing oil to go from the inlet and return ports and back The service ring gap is 10 thou measured on a non worn part of the bore