@pelplouffe I 'm sure someone will correct me if I am wrong? But I believe that the DT125 and 200 share the same frame? I know that the front forks and swingarm are different, as well as the rear shock too. You could do a USD fork conversion on the front and a custom brake caliper mount will enable you to run a larger front disc brake set-up. But for bolt-on straight swap parts this thread will help get you started;
@Calum Haha, for Dune riding right, soft sand, the tread scoops the surface up and away. It doesn't cut into the sand and gives a larger surface area. You should see the boys on the Baja KX500s.. They send it!