Hy Dano&Rose, 139 teeth indicates a six volt flywheel, so a six volt starter would be required, If your truck is currently twelve volt, a six volt starter will still work on that, it just won't take cranking the engine too long, so your engine must be maintained in a good state of tune. Unfortunately the six volt starters had a larger diameter armature shaft so swapping a six volt starter drive into a twelve volt starter is not an option, hope that helps.
