Whenever there is included in any unified district a disorganized district which had established and was maintaining as of January 1, 1965, a public library and branch libraries at the time of inclusion in said unified district, then said unified district may maintain and operate a public library and branch libraries and all statutes relating to the establishment, maintenance, and operation of a public library and branches and the issuing of bonds for the construction and equipping of such library and branch libraries shall apply to such unified district.