anyone know a good way to clean the carbon out the combustion chamber on heads?

Subaru make an engine cleaner.

If they are off the cylinders then try some cloudy ammonia. If the valves are still in pour it in and cover the chamber and leave it for a day. scrub with a brillo pad or equivalent. Old wives tale this to remove carbon.

if you have da heads off then strip da valve's out clean with a wire drill brush & kero finish with a scrower drill pad & kero +clean  valves , then clean & lap valves in ,  inspect for pitting & guide wear if not in good con'd service heads