Buy a gallon of paraffin, and get busy cleaning with some old paint/toothbrushes.
I did this, and then hired an enormous steam-cleaner and gave it a good blast down.
But before I started spraying, I dowsed everything electrical in WD40 (I.e inside all connectors, etc), removed the HT leads and wrapped the Alternator, Battery and Distributor in plastic/clingfilm.
When I finished cleaning, I sprayed everything down again in WD40, and started the engine and got it all good and hot for a bit.
No Problems.
Incidentally, my mate did the engine bay of his Supra at the same time, he didn't bother protecting anything, and that has been alright since as well (once he emptied the water out of the spark-plug recess !).
The other thing I did was remove the cam cover and drive belt cover, rub them down and degrease them, and paint them with black VHT paint.
I removed the Air flow sensor/fuel distributor housing and painted that with silver VHT, and masked off the inlet manifold and did that too.
There is a picture of the result on my gallery page, but it is only impressive if you see what it was like before. ]
My wiring is also terrible and messy (at the moment), I intend to re-route it a bit more neatly, and loom what I can inside black heat-shrink tubing.
Cheers,
Joe