With elk thrown in there my pick would be the Marlin 444. It may not be a 45 caliber bullet it will provide you will very similar energy levels and offer better ballistics than the 45-70 will.

For deer and black bear the standard Remington bullets will work just fine but I would purchase the offerings from Hornady, Corbon, Buffalo Bore, or Conley precision for hunting elk. These four load better bullets that will hold together and penetrate through anything you would want them to.