spark plugg are burnt

63+ remove the spark plug gasket.

"The '63-up heads have a redesigned counterbore at the top of the spark plug hole; the spark plug tube itself seals the plug, and if you use the washer it moves the electrodes out of their intended position in the combustion chamber and interferes with heat transfer from the plug to the head. The '60-'62 heads don't have the special counterbore and need to use the plug gaskets. "

NGK v-power is a quality plug, try em out.