I'd start by timing a very slow mile, and figure that's the minimum time I'll have that bar on my back with about 270. Part of the prep would be dealing with that bar - getting used to holding it at load for extended periods. If you can't hold it standing there for the minimum possible time, you cannot hope to carry it. I cannot imagine how cruel it would feel at a 1/4 mile let alone the final few yards. When Steve first defined the challenge I thought "how is that possible!?" Ahhh, nobody gone more than half way. What padding if any is allowed?