All retirement funds heretofore operating under Kan. Stat. Ann. §§ 72-1726 to 72-1734, inclusive for cities of the first class, and all retirement funds heretofore operating under Kan. Stat. Ann. §§ 72-1780 to 72-1787, inclusive for cities of the first class having a population of more than 60,000 and less than 90,000, shall hereafter be continued under and governed by the terms of this act.