450 marlin is pretty punchy, I mean with the right engineoodling a camming action should handle whatever you wanted, you'd just need surfaces big enough. The thing is that a lever action doesn't necessarily need to be a cam/lever locked bolt. I don't see why it wouldn't be possible to have a multi-lug rotating bolt actuated by a lever. The next question in why would you want a gun that big, and how would you plan on feeding it? Not that big guns always need a reason why, their very existence is answer enough to that question.