A. Nothing contained in the provisions of this chapter shall require any change in the construction, alteration or intended use of any nonconforming structure, under previous Article 21 (Ord. 1957-51) of the county zoning plan (Ord. 1952-III), the construction or alteration of which is begun prior to two years after January 5, 1971, and is diligently prosecuted according to plan as submitted, and further providing that all setbacks and regulations of previous Article 21, as adopted by Ord. 1957-51 and amended by Ord. 1958-7 shall apply. (Ord. 1985-82 (part), 1985)