Quest to getting my Slant six to turn over

Have you measured the battery voltage while trying to start? A weak battery will click or clunk solenoid, but not have enough power to turn over engine. If a battery drops low, to 10 or 11V, it needs a charge, or is bad. Do lights dim or go off when trying to crank?

Also have you tested rotation of engine by hand or wrench, key off of course, to make sure it is not stuck?