Symmetry / single surface / join? / without rebuild?

Model is symmetrical along one axis.

For several reasons including aesthetic, and also closing organic shape with 4-sided surfaces I would like to have one surfaces that crosses the plane of symmetry, meaning cannot use record history / mirror or symmetry tool if my understanding of it its function is correct.

Is there a way to merge two mirrored (for example) 6pt x 6pt surfaces that have curvature continuity into a single 6 x 11 without rebuilding and destroying the surface?

I need a suggestion on how to achieve this from work perspective ideally without having to manually drag the points of a new 6x11 to match mirrors of a 6x6 used to develop the shape.

Have not started on that particular surface yet, so open to whatever the best strategy is.

Solved with GH.