Each town clerk shall, within five days after receipt of an instrument for record, enter the names of all the grantors in a grantor index and all the grantees in a grantee index, in alphabetical order, and cross-indexed as to the party first identified as grantor or grantee on the instrument, the nature of the instrument, the date of its receipt as endorsed upon the recorded instrument and thereafter, when available for entry, the book and page of such instrument or other suitable indication of its location approved by the Public Records Administrator. If such instrument is an assignment of mortgage, collateral assignment of mortgage, subordination of mortgage or other transfer of an interest in a mortgage, the mortgagor shall be deemed an additional grantor for purposes of this section. If such instrument is a grant or assignment of a mortgage to a party designated in the mortgage or assignment as the nominee for another, such nominee shall be deemed to be the grantee of such mortgage or assignment for purposes of this section. If such instrument affects real property, the index shall include a reference to the location of such property, if contained in such instrument. Such general index shall be a permanent public record.