Anderson's backlift ability while using his standard table for many, many personal appearances, was no doubt well below his limit. Strangely though he told the story of being unable to perform the demonstration backlift at one appearance because the specs to build his table had not been followed. He did not elaborate, but perhaps a 2 x 4 was used under the table for reinforcement and would have pressed directing on his spine? Or he literally could not fit under the table. or it was too high off the floor. Who Knows, But it was not for lack of strength.
Anyone with any construction knowledge would have to doubt his story of him backlifting his backporch. There is a photo of that backporch in The Mightiest Minister, and some careful thinking about how such porches were made, and its length, will probably cause doubt that if the center of that porch was raised, say three or four inches (which is extreme for a heavy backlift) then would the ends of the porch even leave the ground?