I have just checked Scottish births on the disc of Old Parochial Records. This can be accessed at Mormon Family History Centers. This disc has no Henry McGlasson but there is a Henry McGlashan, born Moulin, Perthshire, Scotland 5 November 1747. Change of spelling is not unusual as at that date many people in Perthshire were illiterate and unable to speak English. Can you send me any more information about your Henry?