Very rough sand casting. About as rough as 80 grit sandpaper.The flange where the bolts go through is not level as can be seen in my picture. There is about .040" difference from one side of a bolt hole to the other. If left alone, could possibly crack when the bolts are tightened.Surprisingly, I marked the mating surface and run it across some sandpaper on a flat surface and the matting surface is good and flat. I do this all the time when replacing a thermostat and have never come across an original that is not warped.It is going to need some hand sanding and maybe hand polish before I attach it to my clean motor. I would sand and spray some mild acid on it but this may be that type of aluminum that acid will turn black.