A few more observations:
the fact that somebody ran 120-140 mpw and had a little free time in college doesn't convince me that somebody else could run 350. There's a huge difference.
you don't run through stress fractures just because you have a high tolerance for pain. Stress fractures that continue to take a pounding turn into full-on fractures. (although, from the legend surrounding Lindgren, he probably wouldn't have let a broken leg or two slow him down).
if you run 350 mpw, you don't do it at 6-minute mile pace. Guys that win Comrades do that 50+ miler at barely under 6-minute pace, and there are some top marathoners in that field.
you don't do 80+ mile long runs just real casually and eating a few berries along the way. You're going to need a steady supply of food and drink along the way. And you're not going to be able to do that on a regular basis and still come back and blast out hard workouts a day or two later.
I know the criticism I'll get for being a disbeliever: that I've got a closed mind, no imagination, blah blah blah, I'm limited in my running by what society has told me is possible. OK, fine. But if I'm going to believe that somebody did something that nobody else has been able to come close to doing--ie run 350 mpw, including lots of fast running (in high school, no less)--and did it without even thinking there is anything remarkable about it--"oh yeah, I just ran whenever I had any free time, I ran with my heart not my head", I'm going to have to see evidence more convincing than just a bunch of claims based on very anecdotal evidence. For instance, if he could really run basically double, or more, the mileage of his competitors, he should have been able to absolutely obliterate the world records of the time, as well as his competition. I know he was a great runner, but he wasn't head and shoulders above all the rest. Why should I believe he wasn't just training like everybody else pretty much? Because he said so, and those claims were embellished by others, and printed in some books?
And sure, he may wonder why people care what mileage he ran, when the important part was the races. That's true. All I'm saying is, he didn't run as much as is being claimed by some posters on this site. It reminds me of the recent case of Robert Garside, the guy who claimed to be running around the world recently, who made all these outlandish claims for daily mileage, and when questioned said basically that people were closed-minded in their thinking and that he just ran for the joy of it and it wasn't that surprising that he was trashing all these ultra records because he wasn't restricted by traditional thinking. Of course, close investigation found him out in enough lies to make any of his claims doubtful at best.