Cowin is indeed a common name
however the bapt of John Call s/o Thomas states Thomas of Ballacannel - it would appear that Thomas had leased part of Ballacannel but later purchased a parcel in 1796
this he and his wife Ann mortgaged this property in 1816 (repaid 1817) - thus likely John is s/o Thomas Cowin + Ann als Cowin !
thus you have just doubled your Cowin connection
(property deeds + morts are all indexed + many thousands summarised on my cd - see www.manxnotebook.com )

there may well be more relevant deeds