Shortshaft will work, long better
I originally used a short-shaft Johnson 2.3 hp on my DS II, it worked, but would ventilate whenever I got hit by a wave over about 6" unless I sat near the corner of the transom where the motor was clamped. I now have a long-shaft 4 hp Johnson, much better...due to keeping the prop deeper in the water. However, if you will power mostly in relatively calm conditions, I would not hesitate to use a short-shaft outboard. Even in mild waves it will still work very well! The DS I is also OK with a short-shaft, only the DS III will definitely need a longshaft, or else a mounting bracket to get the motor lower on the transom.
