1970 Duster AlterKtion, 4 Link, LS/T56/Turbo and Minitub

The coloration of the threaded portion of the plug closest to the chamber is how to read heat range. You’d like to see 1 or 2 threads colored dark for optimal heat range. Yours look to be right there. Too cold and more threads will be blackened. Too hot and less threads will be.