Above is Mr. L.A. Chappell, the World’s Amateur Heavyweight lifting champion lifting 448-1/2 pounds. A short while later, he improved this lift to 502 pounds! Chappell was a studen of J.C. Tolson, The Young Mighty Apollon.
Note the unusual cambered bar used for the lift. Though it may make the lift a little easier because it does not rotate like a normal Olympic barbell, notice that this bar is also a little thicker. We may possibly have a bar like this available at some point.
If you are interested in learning more about the One-Arm Deadlift, or possibly adding it to your workout, there is a fantastic article about it in The Dellinger Files, Volume I.