A heated debate is brewing between property owners and preservationists over a proposal to designate a large swath of Little Havana as a historic district. If approved by the Miami City Commission, the designation would impose stricter rules on renovations and new construction in an effort to safeguard the neighborhood's unique architectural and cultural heritage. The proposed district includes Calle Ocho (Southwest Eighth Street) from Southwest Thirteenth Avenue to Southwest Seventeenth Avenue,