How to clean carbon build up and TDC?

The only sure way would be to bring the cylinder you are working on up to top dead center on the compression stroke. That is the only time you can be sure the valves are all closed. The easiest way would be to use a long ratchet and rotate the engine with the plugs out. If you are doing walnut blasting, I generally like to be really sure so I add a shop vac to the process, but not the way most do. Pull the spark plugs, attach a shop vacuum on blow to the tailpipe, now rotate the engine over until you can feel the air blowing out of the plug hole. That means the exhaust valves are open. Now blast the valves clean, now rotate the engine to the next cylinder in the firing order and repeat. The added benefit is that the air blowing into the cylinder that way also tends to blow any blast grit out the plug hole if any stayed in the valve seat area.