My recommendation before soaking down the engine compartment and pressure washing is: "Bag the Generator and Air Cleaners" I use grocery store plastic bags and rubber bands.

I spray the degreaser ('engine brite', or whatever) on the warmed engine at home, then drive to the self serve car warsh. Step 1: Pull the distributor and wires. Step 2: Plug distributor hole.. a cork or bag/rubber band, what have you. Step 3: Give it hell with the highest pressure hot water the car wash has to offer. Try to stay clear of the fuse box and relays.

If car wash is busy, push car out when done, or crank it out with the starter. Dry off the plugs, electrical stuff (no biggie), replace distributor and hook the wires back up, and be on your way.

Wear clothes that you don't mind getting ruined. Lots of greasy back splash. Safety goggles are not a bad idea.
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-Matt I ♥ my ♂

I put kerosine in an old spray bottle and use this and rags to clean painted or metal surfaces - old sox are great for getting in nooks and crannies. I put my hand in the sock - after it is dirty, i put a clean sock on my hand and turn the dirty one inside out to use the clean inner surface.

Kerosine dissolves almost all gunk and leaves a residue that fights rust.

Foe plastic and rubber, I use silicone spray that is safe for plastic. Silicone IS safe for plastic and rubber, but cheaper spray cans use a propellant that is harmful to plastic and rubber, and you will not see those materials on the used for list.

This also leaves a residue that fights rust - once and a while, I spray it on mechanicals that look dry..

I take ignition parts off to clean them.

These methods take time, but do no damage. I think that there are many items in an old car that can be damaged by water and detergent that you cannot remove properly- for example, the pivots in the throttle linkage and old fashioned cables

When I got my '64 544, it was VERY dirty as the original engine had worn out and spewed dirty oil vapor over everything for years. It took quite a while just to clean the inside of the hood!

If you don't own a pressure washer, go to one of those "do-it-yourself" car washes, preferably one that isn't crowded, so you don't have a bunch of impatient people behind you. Disconnect the battery cables just to be safe. Or better yet, remove the battery so the battery tray gets clean. Using a spray bottle or a pump-up sprayer soak everything with a good degreaser. A good stiff brush is helpful too. I've had good results with "Purple Power" & 'Mean Green". Let it soak for 15 min. or more if possible, then blast it with the high pressure water, (soapy & then rinse.) I'd remove the air filters & cover the carb inlets. Dry out the inside of the distributor cap & fuse box. I've used this method numerous times, with good results. There's always someplace that gets missed but you'll get 99% of it.

Tommy;

I'd do this after vehicle was recently driven (an engine compartment with a block radiating heat dries faster). Spray degreaser onto specially greasy areas or where lots of dirt has collected in weeping oil, and let it soak for a while...you could even do this days ahead...don't bother covering carbs, their linkages could likely stand some cleaning also (relube after!), just don't blast power-washer or steam-cleaner at air filters...they're only paper, or FuseBlock (it doesn't need extra water in it to promote corrosion), or hydraulic reservoirs for obvious reasons. You don't even have to cover distrib...a little water wont hurt it either...have you ever seen under the hood after a highway drive in the rain?...EVERYTHING IS SOAKED! There is a chance engine might be difficult to start or run rough afterwards, but don't stress, just wipe down Ignition wires and maybe under Dist Cap and that should allow it to run...it should be fine after a short drive and drying out a bit...then the polishing can start, but remember deoiled metal will rust, so paint, wax or protect with clear spray!

Cheers