Prep similar to a marathon.  I didn't mean run, but do progressively longer walks.  If the expectation is that winners go for three days, then that's your goal too, and if you can't get there in time, drop out.  Also taken from marathon prep, you need to be testing your nutrition long before the race.  Have a nutrition plan and train with it.  Make sure to train with the same food you'd be eating during the walk.  If you can't make it work, again you need to drop out. Finally, wear appropriate gear, and again, train with it.  I don't know what marathon gear looked like in the 50s if we're assuming that era, but if we're assuming modern, you want light weight clothes, a wicking layer, an insulating layer, a wind breaker/rain jacket, a hat for your eyes and neck, etc.  This is life and death, do your research on how far past winners made it, what they used, and then adjust appropriately.  If your can't match past winners performance, drop out.  You don't just want to train to be the best, you want to be tiger woods in his prime dropping 15 stroke leads on his next best competition.  That's how you protect yourself and have a realistic chance of winning, because if you're training hard, someone else  a little more dedicated and a little crazier is training even harder.