With respect to an interest in the oil and gas rights which is encumbered by a lien of record, both the person owning such interest and the lienor shall, for the purposes of this Section, be considered as the record owner of legal title thereto; provided that when the lien is based upon an instrument which gives the grantor or grantors in such instruments the right to execute a plan of unitization, the grantor or grantors shall for said purposes be deemed the record owner or owners.