I have a set of stock heads that I took off my car, also the intake manifold, and the valve covers...and they are pretty nasty looking with oil and dirt...can I soak these items in a tub of something and then spray it off with water? what substance is the best as far as getting this gunk off...and is it safe to do it on the heads??? I'm trying to put this motor back together and I want to have things as clean as possible...