Can you still have sticking valves without any evidence of bent pushrods?  And can this be diagnosed with the rocker arms and shafts removed?   I removed the rocker arm and shaft assembly from each head and checked each pushrod individually.   All looked good to the naked eye by rolling each one on a level surface.   As background, I purchased this 56 Thunderbird with a 312 about a year ago.   The prior owner had health problems and the car had been sitting for about five years.  The engine had been rebuilt in the past and can't have many miles on it.   The gas tank was represented as being "cleaned and flushed" but was actually disgusting with a large amount of sediment on the bottom.  I did not try to start it after taking possession until the gas tank was replaced and other fixes taken care of first.   I was finally ready for a test start up.   It caught fire immediately but ran very rough and died shortly.  I tried it a couple more times without success.  It ran before I took delivery but I suspect the damage had been done due to the bad gas tank and varnish deposits in the valve guides.    Thoughts and recommendations appreciated!