As i learned today, just got some parts back from the powder coater/ anodizer. I had about 10 parts (that i thought were all billet) anodized, but one part was cast. It turned black in the acid bath. You can't anodize cast parts because of the impurities in the aluminum. So about 99% of your OEM parts wont take the anodizing. And if it does it WONT be the look your thinking it will be.
My honest opinion, anodizing is for bling*, Powder coating is for longevity. If your part is going to be abused, go with powder coating. There are powder coaters that can make the part almost look anodized. BVC is an advertiser on here, his work looks pretty good. Give him a shout.
~Shawn