Re: new gun/build
If your 280 is already sub MOA, you should be in great shape to get to your 600-800 yard range. How sub MOA are you talking (1/2" groups or 7/8" groups)? What is your goal of shooting at those distances, paper or game? Depending on your answers, I think you will be good to go once you get your Leupold scope and you probably don't even need a new stock.