(1) Unless otherwise provided in the will or trust instrument, the rate of interest upon pecuniary legacies or pecuniary distributions under a trust instrument to which the provisions of General Laws Chapter 197, Section 20 are applicable shall be eight percent per annum.

(2) The rate of interest provided for by this rule shall be applied in computing interest which becomes payable on or after the effective date of this rule. In a case where interest becomes payable prior to the effective date of this rule and the pecuniary legacy or pecuniary trust distribution remains unpaid on such date, interest shall be computed up to such date at four percent and shall be computed from and after such date at the rate provided for by this rule.

(3) This rule shall take effect on July 1, 1980.