The right stem, or an adjustable stem, might make the 520 feel a lot better. Many people discover that they're more comfortable with higher bars. The right stem can get the bars both higher and closer, if needed.

Test riding a bike with an adjustable stem, and riding it at different settings, might give you some ideas. Sounds like you're on the right track.

It probably wouldn't hurt to ask, before buying, if the shop would be willing to swap out the stem.

The challenge is knowing what sort of stem would work best for you -- it's just a matter of zeroing in on the right choice somehow. I think it can be done.

If the rest of the dimensions feel right, and it is just a matter of the top tube being a bit long -- and you like the bike -- it may be a good choice for you. It looks like you're getting some good tips on the other thread too, and that you're well on the way to putting together a very nice touring bike.

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The bars are a big question. There are many different views that can be found on this forum, and on others, including the commuting forum.

It does help to have several different positions, especially on long rides. And many people find that they like having at least one position that is more upright. Heinz Stucke had an interesting solution (by scrolling down you can see the pictures, and there are some more pages that you can access by clicking at the bottom): http://www.bikechina.com/ct-heinzstucke1z.html

Sheldon Brown has done something similar, using drop bars below, and a flat bar above. He used a long steerer tube and two stems. And he installed interrupter brakes on the upper bar.

Some people like riser bars. Others like 'natural' hand positions.

There are many diverse options. Possibly the simplest one is to use comfortable drop bars that are higher than usual, if you can achieve one or more comfortable riding positions that way.