Among different possibilities, I wonder if Atmos.XY.frameExtents (Atmos package) would not be of help here. The description of the node is this one:
"Gathers the maximum and minimum points from a selection of model lines to create an extent frame. Output gives you the frame rectangle, corner points, centre points of frame and centroid of shape. "
Translating the corner points and creating a BoundingBox.ByCorners would follow…
Zhukoven has also a node called 3DSectionBox.Points whose description is this:
“Extract section boxes from desired 3D views, and convert them into Dynamo Min & Max points. Use these points with “BoundingBox.ByCorners” OOTB node to get the bounding box element.”