Looking at 1984... the head tube angle is different, and as I would have suspected, the 520 has a longer chainstay length and wheelbase. This is the norm for a touring bike for heel clearance with panniers and stability when loaded.

The 520 also had some additional braze-ons. Perhaps differing by year, but I believe an additional set of bosses for a water bottle under the down tube, and a low rider mount on the fork. In addition it probably had double eyelets front and rear, and I don't know if your 500 has them.

The 500 is a sport bike, and will not be ideal for touring, but if you have no issue with heel strike, and get everything mounted that you need, then you should be fine. Especially so the more lightly loaded you tour.