If it's just dust, use a soft paint brush and brush it off. Or an air compressor if you have access to one. If it had some kind of oil or such on it and then the dust has combined to form gunk, spray it with carb cleaner or brake cleaner of something fairly mild but will dissolve the gunk, then blow dry it. If it is baked on gunk, (probably not--you said the engines have never been run), then you go to the antifreeze pot method or some other form of more aggressive cleaning. You don't need to use an eight pound hammer to kill a knat. Keep it as simple as possible to do the job at hand.