Oil Pump location will depend on what engine is in it,some are driven off the front of the crankshaft and some are in the bottom of the pan and driven off the distributor.....as for loss of oil pressure that could be any number of things first being poor maintenance and not changing/keeping the oil level where it should be and not changing the filter.....could also be worn out main bearings and just a worn out engine in general......as for the two bearings that were spun am sure there HAS to be damage of some sort if they spun in the block sounds like the engine needs repalced with a Remanufactured one.