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When I got my car the front balancer had slipped and had been riding against the timing cover for quite a while and created a hole. The whole engine bay and most of the underside of the car was covered in grime (maybe that's why there's no rust).
I used Simple Green and a small dish washing brush on most of it. Oven cleaner from the Dollar store works well too, just be careful where you spray it. A few months ago I tried the "Purple Power" spray from AutoZone and it works a little better than the Simple Green.
Cover the carb and the distributor and power wash it with water then blow off the water with a hand blower, I'm doing it for years now with very good results, never used any detergents.