If it's at all possible, soak the stuff you're trying to clean, preferably in a strong, warm solution of Simple Green. Chemtool is another, but these are amazingly foul-smelling, toxic, caustic liquids with a repulsive, oily yellow fetor about them. I'd stick with the Simple Green and a large bucket, if the parts are small enough. A washtub can probably fit an engine block if you're really dedicated. You might have to change the water a couple of times, and you might want to add hot water to keep the temperature up, but that's easy to do.
Heat makes it all work better.
As an applicator, I've found that the best approach is a 1-liter plastic soda bottle with a hole punched through the cap. Best of all, you can dribble a little of the solution out the hole with steady hand pressure, or you can squeeze hard and get a strong spray. I find that the light steady pressure works well with Points 3 and 4. I've had good results with Bondo spreaders on large, flat surfaces like engine bays and oil pans. Soak the area with the hot water-degreaser solution and scrape with the plastic Bondo spreader.