Build an SSGN from the SSBN production line

Should the US Navy build a large force of guided-missile submarines?

If it does, the efficient route is to adapt the ballistic-missile submarine hull already in production rather than create a separate design.

A large missile payload needs the volume already designed into a ballistic-missile submarine. The pressure hull, machinery, and production system already exist at the required scale. Adapting that design would concentrate engineering effort on the guided-missile changes. Reusing the SSBN hull therefore reduces the design and industrial burden of maintaining a wholly separate SSGN class.