Royal Purple makes a cleaner? I thought they only did lubrication fluids.
I use Simple Green. I get the concentrated stuff, mix it up with water in a bottle (but still a high concentration. Wet the slightly warm engine a bit, then spray it with simple green taking care to avoid the fuse box, alternator, and distributor areas as much as possible.
Let it sit about 30 minutes or so, then rinse. Depending on how dirty it is, I may hit it again. If you are REALLY wanting it clean, steaming the engine compartment like dealers do when prepping a used car is what you need to do. It will take a long time, so be prepared.