Thanks again.
Going from the 72 years in Queensland on his death certificate and the ages, I think it must have been him on the Earl Russell in 1864. The father doesn't match though, and was young Margaret still back in Ireland? Maybe the John adult on that was a stepfather, and his father Martin had died. Maybe he's just with an aunt and uncle.
I tried investigating the Simon, because that's such a distinctive name, but didn't get anywhere in Queensland. That was a while ago. I might try again, and look for Simon in Ireland, in Queensland again, and other places in Australia.
Enjoy the puzzle.