Then dont go back, Milled means exactily what Relic1 said, they (mill) or Shave a small amount of metal off of the mating surface where the head meets the block. Normaly when they do this they install a thicker headgasket to compensate for the missing metal, and if you use an OEM gasket it will give you higher compression. Depending on what you want. If I were you I would just leave the head alone, and use that 325 on replacing the water pump and timing belt.