From and after January 13, 1969, former supernumerary judges shall become and be known as retired Justices or judges, as the case may be. They shall receive as retirement compensation, an amount equal to the benefits received by them before that date, payable monthly by the Judicial Retirement System. A former supernumerary Justice or judge who stands assigned by the Supreme Court to active judicial service duty shall receive as his annual retirement compensation, an amount equal to seventy-five percent (75%) of Seventeen Thousand Five Hundred Dollars ($17,500.00) payable monthly, for so long as he continues in full-time active duty under such assignment.