Mary Newcome Schleier has kindly confirmed the attribution and points out that this is related to the painting in San Stefano, Larvego dated 1777 commissioned by Giacomo Durazzo. The fullest account of David as a draughtsman is in Mary Newcome's recent article Drawings by Giovanni David, Master Drawings, Essays in Memory of Jacob Bean, 1993, XXXI, pp. 469-79