I have no record of an earlier John McGlennon (or similar) - what info makes you suspect a Manx birth - the name is not Manx - probably Irish - if Roman Catholic then at this time it would appear that any records might be held in Dublin (I have 1812/3) but look at www.manxnotebook.com/parishes/rcath/rc.htm

(btw I think the previously mentioned John is buried in Andreas in 1830)