For a guy who ran 3:53.43 and 47 something 1:47.74 is pretty crappy. Take this predictor that has been proven to be accurate to at least .5 seconds either way.
alans 400 time: (47.5)/5*6=57.0. Then take his mile time divided by 5, 3:53.43/5=46.69. then add up the products. this adds up to 1:43.69. obviously way off, but if you take the PRs of other runners and put them into the equation it comes pretty close (even your own PRs). You could make the case that webb wasn't really trying to run fast at that time because he was winning nationals with 1:47.7, but even after going pro his 800 PR was 1:46.09 in 2004. What I'm getting at is that I think what is generally accepted as Alan's 400 from high school is way off. I think he ran more like 49.5-50.0 and somebody wanted to trump up his speed and accomplishments so they exagerrated his 400 time.