[wrndln]

I think you would be better off laying some sandpaper on a very flat surface. I had a glass company cut and edge some heavy plate glass. Plate glass is ground and polished to an extremely flat surface. By placing some sandpaper on the glass, you can get a very nice flat surface on what ever you want to make flat, by moving the part back and forth. I have done this on goosenecks and water return pieces that bolt to the engine. You can tell when the parts surface is flat when the whole surface is shinny. It takes a little time, but it worked quite well.
Rusty Nelson