I've done that job a number of times. You have to have a jig to support the motor. I built a simple A-frame with lumber--rests on the inside edge of the fenders with a chain to the front motor hoist hook. You can then remove the 3 nuts from each of the motor mount bases. With the car elevated and jack stands placed at the jacking points, support the subframe with a jack and then from inside the engine compartment remove the subframe bolts-2 on each side along the frame rails. When you lower the jack the subframe should drop enough to wiggle the oil pan out--it's a tight fit. It is possible to get the pump changed without totally removing the pan but you need small hands to slip into the gap--not like mine. Most important is to be sure you actually need the pump. The oil pressure switch is easy enough to reach--remove it and temporarily install a mechanical gage. If you know someone into british sports cars they're bound to have a used one laying around--new plumbing parts are cheap. Remember, the wiring to the oil switch is prone to peeling its insulation and when shorted the light comes on.