The front main seal is a round lip type pressed in seal.  there is no reason to pull pan.  I changed one in the truck a long time ago.  It was not he easiest thing to do, but possible.  Remove fan and front crank pulley and pry out old seal without damaging front cover.  I can't remember but I might have pulled radiator and grille to get access to drive new seal in.  I then used a large hollow driver that fit over snout of crank to drive new seal in sqaure, but if your good with a hammer and punch you may not need a driver.  Air conditioning will complicate this if your truck has it. 
