Leslie Quilliam in his Gazeteer says Crammag,Lezayre is at map reference 371884 & as you say the croft is a ruin /a tholtan now on the southern edge of the "new" Sulby reservoir.A Cowley was one of the leaders of the Sulby Cossacks who protested the enclosure of the mountain land. Crammag river/stream enters the reservoir close to the tholtan.[Car needed unless you are a keen walker to walk up the road through Sulby Glen.]
Is the Close also in Lezayre?