Like Michael, I powder coated mine. It is wonderful and more importantly for me, it will stay that way. I have never had any luck powder coating aluminum with clear and cast parts are even worse. I know this is mag, but should be similar. The base metal continuous to "bloom" underneath the clear coating. Not sure why and yes it was done professionally. So after a couple of years, it becomes mottled. With steel, I have no problem with clear.
I used a Bengal silver powder (no clear on top) from Tiger Drylac. Most pro shops will have it. It looks pretty darn close to cast aluminum. Not bright aluminum like many colors. It has a dark fleck in it that gives a cast look. It is not a high gloss, but glossier than bare aluminum. The gloss does fade a bit over time.
In fact I have powder coated many of these parts, water pump and thermostat housing, etc. It gives a very uniform look to the engine compartment. You have to know what to mask off when doing the later parts or you will get into trouble.
