Hello - I made new (red) curves - looking at the centerline curve (with the curvature graph) , it has a ton of points but looks like it is a straight line in the middle, sloped, and two s-shaped blends out to more level lines, so I made it that way - a line and two simple curves:

I made new cross section curves - these look like they are tangent across the centerline and tangent to the vertical sides - not curvature continuous, again, looking at the existing curve’s graphs for confirmation.

I used slightly edited copies of the three centerline curves to finish off three rectangles:

`EdgeSrf`

makes all three surfaces.

Then ExtendSrf the ‘front’ one(s) and trim like so:

Then create another edgeSrf in the same way - four clean, simple and matching-on-opposite-sides boundary curves. Note they match here even though the point count differs because they are all single span curves.

Then MatchSrf on all edges - for Curvature back to the trimmed edges, for tangency to the lower surface and for tangency with Average across the centerline. I found I needed to InsertKnot > Automatic a couple of times to get a good final match to the vertical wall,

-Pascal