'73 340 horsepower

Since ya'll should know more about this since I'm more old school (54), horsepower-wise. I have a '73 340 longblock under my workbench. Would I be better off rebuilding it (I'm going to run carb, elec. ign., etc.), or go with a newer Magnum or 5.7? I'm using it in a 72 Duster w/4-speed and 2.76 gears for now.