How do I clean this gunk!

RedFish said
In the good ol days we would take them to the car wash. Their high pressure sprayer would get'er done. According to EPA we aren't supposed to do this at home if the run off can go to ground water, and better not get caught at the car wash.
I use a screw driver and compressed air to break up and remove the majority, then oven cleaner, then high pressure rinse, then brake parts aerosol, then paint.

I still use this method. They have grease traps to collect the gunk. They also still have an engine degreaser setting that actually works. You coat the parts and let them soak then hit them with the high pressure wash. Just watch out for back spray. Can make you not only wet but nasty with the gunk as well.