Stuck valve
 

This concerns my 67 230s (180.947). About halfway on a 15 mile trip, a valve noise developed. It is a clear tick that can be distinguished as one valve possibly stuck open. I would like to try and free the valve. Does any one have any suggestions before I go out and beat it with a leather mallet? I am going to assume carbon particles are causing the blockage. I have also heard that dumping diesel into the carbs with the engine running will burn with a higher temp and possibly removing the excess carbon.

More likely you have a worn rocker arm or an adjuster that has backed off. Find which valve adjustment is wrong and go from there.