To add to what nun and vik have said, for your planned trip I'd also look to set the 520 up with the widest tires as possible (allowing for a little wiggle room in case a wheel comes out of true). Wider tires won't slow you down noticeably but will make a big difference when the pavement fades away.
I don't know if the 520 frameset was changed to address this for the new year but it used to be a challenge getting big tires and fenders on the front.
Have fun planning for your tour!
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Ron - Tucson, AZ