I ended up rebuilding the entire lofted body, which is basically the whole middle section of the part. Doing so allowed me to modify it down the line, which is really useful when building NURBS surfaces. After making the outside shape, I ended up needing to tweak it a lot to avoid collisions with later features. Accommodating these changes is hard to do, though - you kind of need to know what the part is going to look like before you start. It's a real chicken-and-egg problem. What usually ends up happening is that you don't do it right until you've rebuilt the whole model three or four times, which is about where I'm at here :)
It's hard to describe, but the upper section is hollow. I also spent a while trying to optimize around shared surfaces, so the window upper & lower walls coincide with features that I already needed on the part. The one thing I'm not particularly happy about is the seatmast clamp at the bottom of the part. The details are a little different, but overall it's designed the same way it would be if the part was welded. This part is going to be 3D printed, though, and I'd prefer to find a way to build the feature in a way that directly addresses its manufacturing method.
But overall, the part is definitely forward looking. I'll post a section view later, but for now just take my word that most of the middle of the part would be impossible to make by any other method than additive manufacturing. Also, right now the topper body (just the gold part, not including hardware) comes in at 74g, and I suspect that with a little work I can shave that even more :)