If you drop the pan, you will need to drop the valve body also. I usually drop the tranny crossmember and tilt the back of the tranny down with a floor jack to give me additional room. That way you don't have to drain the tranny fluid or have a big leak from the tailshaft (leave the driveshaft installed). Remove the linkage (kickdown and gear selector), clean the area to keep stuff from falling in when you remove the seal, and pry the seal from the case with a small screwdriver. To install the new seal, lube the seal lip with tranny fluid. Get a socket that will fit the metal part of the seal and clear the shaft, and tap the seal into place. Reinstall the gear selector and kickdown linkage. Top off tranny fluid as necessary and take it for a test drive...