Bike fit and other proportions aside, if you're going to make substantial changes to the bike (components, etc.) and have to also procure the upgrades then it might not be worth it in the long run.

It sounds like you had specific reasons for leaning with the LHT in addition to wheel size (26" vs. 700c)... look at your 'mission'; what kind of touring and where you'll be riding. Perhaps the LHT is better suited for the type of riding you want to do as compared to the 520.

As mentioned previously... some photos of the 520 would help in assessing its value.