Take a look at the NEF Handi rifle. The 45-70 neing a rimmed vartridge work real well in the NEF. A new one would run about 200-250 follars. You can also send them in to NED for addition barrel pretty cheap. The actions are strong enough for yje Marlin level loads and will handle the lower level Ruger loads as well.
I took a 500 + lb Black bear with mine using the 350 grain Hornady RN.