When I cleaned the carbon off the Pistons, I tilted the engine whereas the carbon would fall to the floor rather than into the space between the piston and cylinder wall. Maybe placebo effect, but I felt it didn't allow any dust, etc. Into the rings/walls. Honestly the only thing I would worry about is the deck, you don't want to use amything harsh that may scrape, scratch or damage block or head surface. I used as mentioned, scrapers, wire brushes, WD40 (great oil/grease remover) then simple green with lots of throw away rags. Just go slow and it'll get clean...
