Start with turning the engine over by hand carefully with the spark plugs out. Taking the valve covers off and watching the rocker arms move is not a bad idea. Slow and easy is the word. If it binds up or starts to turn hard somthing is happening and or somthing may be stuck. ATF will not hurt the engine, however a couple of squirts of engine oil in each cylinder will help with lubracating the cylinder walls and imporve any kind of compresion you may have left. The carb may need to come apart and cleaned out along with the fuel lines and fuel tank.
