On this you will probably have to partially unbolt the front differential and let it hang, also you will have to remove the steering rack and pinion, then you can remove the oil pump. (Of course you will have to remove the oil pan also.) This is what I had to do recently on a '01, but I also drive a '99 and it shouldn't be too different. Sometimes you can get lucky enough for it to drop low enough you don't have to remove anything but the oil pan.