Wouldn't want to be changing the postion of the wheels in the dropouts if there is no way of fixing them in that position.

Concerns would be getting the wheel in straight with no guide after changing tubes, and the brake position.

Looking at the R500, can't see any rack mounts on the rear stays, so are you carrying much?

if light weight touring, 25mm tires will be sufficent, and fit your frame, the Marathon Plus, although good, are heavy.

Would be worth asking this in the touring forum