Yes, they are aluminum, got them from a fellow in New York back in the mid 1990s who did them for Hot Rods.  Very reasonably priced and yes, I would do it the same.  I initially added the louvers when I was having oil temp problems (before I moved the oil cooler up under the spinner).  They now probably help on the hottest days and after shutdown. 

   Here is the URL http://www.norwich.net/canfield/canfield/samples.htm  you might look in his "samples" section and see examples on an aircraft.

You can get various SS and chromed louvers from marine supply places.

I wish I had known about the ones from Lancair before I went the trouble of making my own fiberglass version.  These are in the top of my cowling.

Al