[kerneltugboat]

I did a surge tube, a muffler and an exhaust port with a flapper. I do not have an inboard, but a jackshafted I/O which is similar in regards to engine location. I do not have a riser on my D6, but even with 12 guys in the boat and the motor off I did not have any problems. You may not need the muffler, but I do recommend the surge tube and the flapper. If you want to see mine feel free to check mine out in Chatham. I will look for some pics.
There is also another 23 inboard in Chatham with a D4, you may want to cheeck out what he did (Dmese on the site). He had a special exhaust made from stainless that was pretty cool, but I don't remember if he did a surge tube or a riser or both.

Dan