In the spirit of our small airplane landing on a carrier question, I decided to up the ante slightly in a couple of ways.
Let us say some enterprising foreign navy has found a small flattop under their Christmas tree this year, and is in need of some aircraft to fly off it. Of course, tactical aircraft are a necessity, and to that end, they could obtain some used A-4s as a starting point for their fledgling naval aviation branch. However, there are other important aircraft on a carrier deck, one of them being the Carrier Onboard Delivery plane. A bright young naval officer there decides "Hey, we should see if some small civil planes might work for what we need", and does a bit of research, stumbling upon the DHC-6-400 with its widespread support base, ease of maintenance, good STOL performance, and current production availability.
How much modification would our enterprising foreign navy need to ask Viking Air to do to their order of DHC-6-400s to be fully usable from a carrier deck?