from the intertubes memory hole:
The standard Trek 520 has 11-32 in the back and 30/42/52 in the front. This gives a gear range of 24" to 128".
not sure if that's what you got...........but it's nuts for an old guy to tour with.
i'd prefer 16-18" low gear.
not worried about the high gear. coasting is fun. but 95-100" is fine.
should be a piece o'cake to switch out the front crank with a 26-36-46 and the rear with a 14:34.
your mechanic can confirm your deraillers will handle the chain wrap.