Thanks everyone for the comments/suggestions! I hope to put some cleaning time in over the holidays! Happy Thanksgiving all!

For the Olds W-cars, we have aluminum intake manifolds. I've had good luck with vapor blasting the aluminum. It comes out somewhat bright at first but over time the brightness wears away and it looks more like a stock aluminum finish.

Vapor blasting is the best I've seen, I agree. But he doesn't want to remove the manifold from the car so...

Clean the aluminum intake the best you can. Then use Hi-Temp aluminum paint. Spray a small amount into a container and add lacquer thinner to thin the paint out. Take a stiff bristle brush, dip the brush into the mixture of paint and lacquer thinner and rub the solution onto the intake manifold.

Nice tip on the bristles of the brush , what brand oven cleaner are you using? There used to be a brand Mr.Muscle it would remove the car lot under hood paint jobs in the old days..