It sounds to me like your starter/flywheel problem is your ring gear on the flywheel, your engine has a tendency to stop in the same place, therefore it is started in the same place on the flywheel, after 50 or so years the teeth on the ring gear will start to wear and then will not fully engage with the starter drive gear, if you turn the engine over by hand past the wear points it should engage the starter, the cure is simple replace the ring gear, the process is a bit of a PITA, you will have to drop the transmission, remove the clutch and the flywheel. Keep in mind that you may have a six volt starter and flywheel on your truck, there is a difference from 6 volt and 12 volt when it comes to starters and flywheels.
