I only see one “surface” in the file - it’s actually a polysurface - but if you mean creating a solid from it and a copy which has been moved some distance away, I would just create the top and bottom planar surfaces (Plane, SrfPt), join all and Cap.
Gumball Extrude will work in one shot, but I don’t like the surfaces it leaves on the ends when extruding tangent to the arcs. You could extract those and re-cap the object to have nicer planar surfaces there.
If the input surfaces are both parallel to some of the World axis (or a custom CPlane is created along the surfaces), then using “Bounding box” may get you a quick box to split with the former to create a solid object with the desired shape.
One potential problem with that approach is that “Bounding box” is inaccurate and may lead to some small deviations.