Well in our shop we always used brakeclean. It should do the job. That foam engine cleaner in a can, aint worth much really. My cousin bought it, used it excessively with a metal brush and didnt get much off. The main thing you got to worry about is getting it out of where the oil goes, more than getting it out of the water jackets. But Id get like a tub of brakeclean and get a container that is long enough for or 2 heads to sit in. Put them in it for like 6 hours. Id also probably use a part cleaning brush, if th oil is caked on the outside of the head(for appearance). You can probably hold the valve covers down for like ten seconds, than use the brush to get it clean for the most part.