There are 2 versions of the wet sump, the 6 and 6a. The later -6a- has a hump on the top of the outdrive. The 6a rotation is converted in the upper. The 6 is rotated/counterrotated in the lower.
All of the wet sumps from mercruiser have the non swept skeg. Herring can convert to a swept skeg for 5-7k (verify this number as it is from my memory).
The cost to convert to dry sump is approx 5k. Check with Weismannn or Cobela.
I've heard the dry sump is worth 7 mph on a cat and the swept skeg is worth 3 mph. I personally have no data to verify this.