Remove the oil pan. Place a large drain pan under the engine. Unbolt the pump from the rear main bearing cap. Lower the pump and extension shaft from the engine. Before installation, prime the pump with engine oil. Pour oil into the pick-up while the pump extension shaft is turned. Attach the pump, extension shaft and retainer to the main bearing cap. While aligning the pump with the dowel pins at the bottom of the main bearing cap, align the top end of the extension shaft with the lower end of the oil pump drive. When aligned properly, it should slip into place easily. Install the pump mounting bolt and tighten it. Install the oil pan and add oil.