Turning a 73 Dart into a 72

Well after struggling to get this thing running right-rough idle,stumble.I decided to tear into it once again.found the lifter for the #7 exhaust was tore-up.Strange as all the others look fine with a nice swirl pattern.Well I figure the whole block is probably full of metal shavings. So it's definetly coming out.I wasn't sure what to do next but I was able to find a low mileage rebuilt 360.I'm going to pick it up tomorrow morning.I will post pics.I'm hoping this mildly built motor will salvage My project.