Perhaps this is a good time to point out, once again, that the 'about' dates are not good enough. Francis has explained this very recently on these Boards.

The names John, and William are very common, in fact there seemed to be very few Christian names in use. The Manx pattern of naming children makes research from afar difficult. The IGI is good, but unreliable.

Perhaps joining the Isle of Man Family History Society may be of benefit?