Mark, of course I have no knowledge of your background, but I will offer the analogy of amateur car racing. Many of us begin with a factory Chevrolet, Ford or Mopar block, rotating assembly, and cylinder heads. We then spend hundreds of hours porting, machining, preparing, and fitting the parts together. Our labor is usually free, although inevitably you will likely need to pay a machine shop for some work. You put all your heart, knowledge, and wizardry into it, try to be thrifty, and then go racing. All sanctioning body rules aside, your engine will never produce the horsepower, or have the longevity of one built with a racing block, forged or billet rotating assembly, and most importantly, will never flow air like TFS, AFR, or similar racing cylinder heads. Are you racing? Yup you are. Are you winning? No, not in the scenario I have set out. In addition, your engine created with factory parts will never have the resale value of a true race engine.
For me, and some others, a trued Remington action is fine. I do not compete. For your intended use, a custom seems the best choice. Later, if you decide you don't care for BR competition, you can sell it and get much of your investment back. In the meantime, you have the equipment to give you the potential to be competitive. One way to make your choice of a custom action is to look at the equipment lists of the national competitors. The actions that they use will be listed.
Best of luck in your quest, Peter.