1.736" from the top flat surface of the housing down into the bottom of the yoke where the plunger seats.
All D318, D315 etc are the same.
Measure at TDC on compression stroke. the lifter will continue to rise as the engine rotates past TDC.
SJ used to recommend decreasing the setting to compensate for any measurable wear on pump plunger length and lifter yoke bearing surface. Plunger length is 2.6575-2.6577 max wear of 0.005"