If any two or more persons have by their mutual will massed the whole or any specific portion of their joint estate and disposed of the massed estate or of any portion thereof after the death of the survivor or survivors or the happening of any other event after the death of the first-dying, conferring upon the survivor or survivors any limited interest in respect of any property in the massed estate, then upon the death after the commencement of this Act of the first-dying, adiation by the survivor or survivors shall have the effect of conferring upon the persons in whose favour such disposition was made, such rights in respect of any property forming part of the share of the survivor or survivors of the massed estate as they would by law have possessed under the will if that property had belonged to the first-dying; and the executor shall frame his distribution account accordingly.