I removed my oil pump, rebuilt it & re-installed it without removing my oil pan.  Step one:  drained the oil & removed oil filter.  Step 2: unbolted & removed the cover plate of the oil pump very carefully, pulling out the gears & drive shaft from the distributer.  Step 3: remove the 3 bolts holding the pump body to the block.  Step 4:  Loosen the big nut holding the oil line to the oil pan.  Lower the pump body pulling it out of the oil line when it is dropped to enough clearance.   Step 5: Rebuild pump & install in reverse order.  Start the pump body bolts & before tightening up,  use a pump oil can ,putting oil into the pump.
  Step 6: Fill the oil filter with oil & the rest of the oil back into the engine.  Start engine & give it a little time to start the suction. It took from 10 to 20 seconds.   
  Hope this helps with anyone needing to change or rebuild your oil Pump !