Got get a couple cans of Gunk engine degreaser (about $2.00 per can), soak the entire engine. (Read the directions) Works best if you have a pressure washer but if not, hose it down using as much pressure as you can get. You may have to dry out the distributor cap when you get finished but no big deal. Hose the heck out of everything.
I agree with Ray, you can use aluminum foil to cover the distributor and carb and other openings during the process. It also helps if the engine is warm.
i use oven cleaner myself. seems to clean a little bit better. and if u have a car wash close, drive it there and clean it up.
If you have heavy oil deposits caked on the block or elsewhere it will help to scrape off as much of it as you can with a putty knife. I do this whenever I degrease an engine. Also, after I spray on the Gunk and it sits a while I'll use a brush on some of the stubborn stuff before rinsing the engine off with the pressure washer. Be prepared to have an oil slick running out from under the car when you are done.
Getting moisture in the dist cap because it won't start. Just keep a can of wd-40 handy. You can spray the inside of the cap and it will disipate the water.
Just be sure not to get water in the carb or the distributor. For both parts I cover them with a gallon sized ziplock bag and either tie or tape the opening closed as tight as I can. If you take the oil cap off clean the surface around the opening as best as you can and put a couple of strips of duct tape over the opening. Do the same with any other openings you don't want water to get into. The spark plugs and wires will get wet, but that wont prevent the engine from starting back up. You may also want to wash the front of the car afterwards because the Gunk and crud from the engine will most likely get all over the fenders and grill.
Cover your alternator tooDont hose down electrical components like the voltage regulator either.Get the engine up to operating temp before you soak it with de-greaser(works better hot)garden hose and scrub or go to the do it yourself car wash and pressure wash it as stated before.
I use a putty scraper to get the heavy suff off and a parts washer brush and a toilet bowl brush. An old tooth brush gets in the tight spots.