A participating local district may, by filing with the board a duly certified copy of its action, provide, in lieu of any other retirement benefit in this Part, special retirement benefit plans in this section. If a member retires after becoming qualified to retire under section 18451, his retirement benefit will be computed in accordance with section 18452, if that amount is greater than the amount computed under this section. [1985, c. 801, §§5, 7 (NEW).]