I just pulled the oil filter adapter off this afternoon looking for a gasket problem. My question has been answered. What you see down the bore is NOT a seat for the relief valve plunger, it's a stop. And the diagrams in both the Dodge FSM and the Cummins repair manuals about how the valve functions are grossly inaccurate.

"We live in a time when intelligent people are being silenced so that stupid people won't be offended".