Although Chilton says to remove the engine for removal of the oil pan, it also says this.
Removal & Installation
Pan removal is possible with the engine in the vehicle on some of the powertrain combinations covered by this manual. If it is possible, it will often require the removal or repositioning of components including, the steering linkage assembly, the forward drive axle and crossmember (4WD) and/or the engine mounts. It is a difficult and tedious task to remove the oil pan with the engine in the vehicle. The chances of contaminating the bearing surfaces or damaging other internal engine components is great. Also, working under the vehicle with the engine jacked up in the frame puts you at great risk for great personal injury. Therefore, it is desirable in most cases to remove the engine in order to gain access to the oil pan.
I imagine though, the oil pan could be changed without removing the engine even if you have to unbolt the motor mounts jack up the engine and place 2x4 pieces of wood between the block and frame to keep the engine up high enough to remove the pan.
For the complete Chilton instructions ,click here.
I might add, if there is a distributor at the rear near the firewall I would remove the cap and rotor so it dont get cracked while jacking the engine. Also, remove the bolts from the fan shroud is the fan will hit the shroud when jacking the engine and either remove the shroud or let hang free.