Did mine by lightly blasting with low pressure glass beads then 0000 steel wool to put a light shine in the peaks of the fins to put a very light shine on the flat surfaces. Had to do it twice to get it where I wanted. The key is to not rough it too much in the blast cabinet. I used about 40 psi, just enough to pick up the media and stayed about 8 inches away from it. Just enough really to clean the surface and even out the surface.
I then followed up with the satin finish Ever-Brite to seal the pores and make them easy to keep clean.