I found the baptism transcriptions as well as copies of the original baptism records for four children of Daniel “Shaughnessy” and Mary McGrath, including the baptism for your John, who was indeed baptized in 1845. If you do not have these baptism records I can send them to you in a follow-up reply. I also found Daniel Shaughnessy in an Irish property tax record known as Griffiths Valuation. I can send this record to you as a transcription as well if you do not already have it.
Once I hear back from I’ll start compiling the records mentioned above and send them to you as soon as possible.