Permitted modification of minimum lot area and width. No lot in a cluster subdivision shall have a lot area of less than 57,600 square feet measured within 320 feet of the front street property line, nor shall any lot have a lot width of less than 180 feet, provided, however, that on a cul-de-sac or curved street, each lot shall have a frontage along the front street property line of at least 75 feet and a lot width of at least 180 feet measured along a line 100 feet from the front street property line. All other setback and bulk requirements for the R-2 Zone shall be met on each lot within the cluster subdivision. In a cluster subdivision which will be served by public water from an off-site source, the requirements of Subsection 16-15.4 shall apply to the development.