Liz It would seem your G grandad's birth was not
registered / not compulsory in IOM until after 1878.
Have you looked for a possible baptism on IGI/familysearch.org ?
At Registry pay £3.00 to look at the death register
for the year he died/ you don't have to buy the
cert. If you are lucky and the ledger is not needed by the officer or another member of the
public you can read it all & if the same reg. distict
is relevant you can find other info /family for free.