that black podwer is most likley from ur belt frying is should smell burnt replace ur belt and take a wire brush clean any imperfections on the pulleys the rubber will accumulate over time causing constant belt ware. pull the heads and relap the valves if u dont know what i am talking about just ask ur auto parts store they will hook u up pull the valve cover and check ur springs and rocker arms just make sure everything is secure and change the oil this seems like a valvetrain problem but i cant know without being there to see it. but just go through the whole engin and buy a sbc engin overhaul manual i like the haynes one