1981 Chevy C-10 pickup
427ci tall deck motor
heads are date stamped 1973

Ok after a little bit of research this morning, I managed to find some literature that says..."All cast-iron heads made prior to 1970 use 13/16 inch hex plugs with gasket, 3/4 inch reach." Then, obviously, says that all heads built afterwards use " small 5/8 inch tapered plugs with a 1/2 inch reach. Since being purchased, I have been using gasketed 13/16 plugs, my thoughts are that maybe im using the wrong plugs... Any final thoughts on this???