Hi Joe,

   The main difference (the expensive parts) are the side seals, the corner seals and the oil seals (steel parts) and springs.   These parts are often in perfectly usable condition at overhaul time so measure them properly and if they are in good shape, go with the much less expensive Basic Overhaul kit.   There are a few other things like the oil pump drive chain in the Master Kit as well but those are the biggies.

 

Tracy Crook