Rhodesia SG255u One Pound BLOCK on a Land Grant document

1917-20 One Pound Head Die IIIA block of four in deep black and reddish lilac on Land Grant document.  Cancelled by LAND GRANT SERRLEMENT DEPARTMENT SALISBURY violet cachet signed and dated over the stamps in red ink.  Also signed by the Colonial Administrator on reverse.  A rare multiple of this printing and a handsome display item. SG 255u. Ex Spivack and Brickman