To clean it once or twice a year, Simple Green works good, on a lukewarm engine. I use foil to protect electrical stuff from water and avoid direct spraying. I just use a garden hose and a shower type spray head. I start and run the engine immediately after. Water spots are tough though.
To keep it clean, I clean under the hood as much or more than the interior passenger compartment. Mostly it's just 'dusting'. The kids think I'm anal, and the wife gets jealous and starts demanding attention.
I need to do the '91 LSC as well, it is 'filthy' in a relative sense. I'm afraid though that will put her over the edge(the wife, not the car).