On designated retail streets, as shown on Map 4 in Appendix A, for buildings developed or enlarged after August 27, 1998, where the ground floor level of such development or enlarged portion of the building fronts upon such streets, uses within stories on the ground floor or with a floor level within five feet of curb level, shall be limited to only those uses permitted by the underlying regulations and Section 91-111 (Additional uses in C5 Districts), other than automobile showrooms or plumbing, heating or ventilating equipment showrooms, or any of the uses listed in Use Groups 6B, 6E, 7C, 7D, 8C, 8D, 9B, 10B, 11 or 12D.