Section 76-203 shall not be construed to extend to a letter of attorney or other instrument containing a power to convey lands as agent or attorney for the owner of such lands; but every such letter or instrument, and every executory contract for the sale or purchase of lands, when proved or acknowledged in the manner prescribed by statute, may be recorded in the office of the register of deeds of any county in which the real estate to which such power or contract relates may be situated. Such an instrument, when so proved or acknowledged, and the record thereof, when recorded, or the transcript of such record, may be read in evidence, in the same manner and with the like effect as a conveyance recorded in such county.