All municipalities which shall have heretofore adopted the provisions of the act entitled “An act relating to, regulating and providing for the government of municipalities, except counties, by a municipal council and a municipal manager,” approved March nineteenth, one thousand nine hundred and twenty-three, and all municipalities which shall hereafter adopt the provisions of this subtitle, shall be governed by a municipal council and a municipal manager in the manner herein in this subtitle set forth, but no municipality governed by the provisions of subtitle 4 of this title (s. 40:70-1 et seq.), shall institute proceedings hereunder for the adoption of this subtitle unless and until said subtitle 4 of this title, or the provisions of the act entitled “An act relating to, regulating and providing for the government of cities, towns, townships, boroughs, villages and municipalities governed by boards of commissioners or improvement commissions in this state” (title as amended), approved April twenty-fifth, one thousand nine hundred and eleven, or both said subtitle 4 of this title and said last mentioned act shall have been operative and in effect in such municipality for four years.