It was common to have another child named the same if the first named died. I don't know if this happened elsewhere but common for sure in Ireland.
The Northern Ireland telephone book has 4 ROCK's listed
3 in a place Tassagh and the other Dungannon.
These come with addresses and postal codes.
13 McSorley's, 2 Dungannon.
Of the children Peter would be the next easiest to trace.www.census.nationalarchives.ie
No Simon or Peter.
There is a Simon Rock in business in Armagh in 1885 but my image viewer isn't working. Will check at home.