I'm in the process of cleaning up an intake setup myself. This one I've had for over 25 years, used to run it on my '57 chevy 2door HT but it has been siiting (and getting grungy) for the last 20 years or so. I soaked the intake in a 5 gal pail of diluted muriatic acid (hydrochloric acid, same thing). The intake is too long so I just soaked one end until I was satisfied then flipped it over. Works great on cast iron also but you need to neutralize the acid after done. I first power washed the parts then soaked in a pail of water with baking soda in it. Stir often, then power wash again. Here's a before and after.

http://www.telusplanet.net/public/tetachuk/intakebefore.jpg

http://www.telusplanet.net/public/tetachuk/intakeafter.jpg