I really like a soda blaster for this type of cleaning. It's much less aggressive than bead blasting so it doesn't rough up the aluminum and the leftover grit is water soluble and can be rinsed off with water. It leaves a nice finish on aluminum parts. You can get a soda blaster for pretty cheap from Harbor Freight.
I'm getting ready to soda blast a bunch of aluminum KDX parts myself.
Riding around here there is heaps of clay in the soil. The clay mixes with water and sits in puddles of caramel consistency. This water sprays up on the engine where the water evaporates and leaves the clay baked to rhe engine and other components. I generally just blast the loose stuff and live with the rest.