4/1/2015
I have found another record for John Gill and now know he was NOT John McGillicuddy. John Gill eventually ended up in Tasmania and was pardoned while John McGillicuddy remained at Darlinghurst.
I have also acquired a copy of a book entitled "The Convict Ships" by Charles Bateson, second edition 1969. The book is out of print but available from book dealers online (for a handsome price).
The book confirms that there were two different convict ships with similar names; the Hydrabad and the Hyderabad, Both ships made voyages to Norfolk Island, arriving in 1845.
The Darlinghurst records state that John McGillicuddy arrived on the Hydrabad not the Hyderabad, But the Hydrabad's convict records do not list him. The convict records for the Hyderabad seem to be missing. At this point, I am inclined to believe that the Darlindhurst records must be in error with respect to the ship's name and that he was in fact on board the Hyderabad.
So, I seem to have arrived at the genealogist's brick wall. I am unsure where to search.
I want to thank everyone here who has tried to assist me. You have been very kind.