The BASICS of a dirt setup include softening the springs, raising ride height, increasing pinion angle, and changing to dirt tires. For a one off race, you can run federals (the more tread left the better). Uncut tires are better than cut.
We also put mesh screens on our grills to keep larger chunks of mud from getting caught up on the engine.
There are a lot of dirt setup tips on the site that should get you close.
As far as clean up goes, clean and wax the body before hand. Keeps the dirt from sticking as much (it will stick no matter what). Be prepared with a pressure washer for clean up afterwards.