I located the marriage record on December 15 1832 in the Dunshauglin RC church. Spouse was Ellen Murtha according to the transcription.
The entry on the parish register is very faint (see bottom right) https://registers.nli.ie/registers/vtls000635134#page/14/mode/1up
The parish register for Dunshaughlin has a gap in baptismal records from January 1843 to January 1849. Likely Dowdall children were born in this gap period.
Roots Ireland did not have the record for James but I did find a baptismal record for a Francis Dowdall baptized January 14 1850 father William and mother Eleanor Murtagh.
There was also a John baptized June 27 1851 mother was shown as Eleanor Murtha.
Both records showed Culmullin as the address.
I went back to the register and found the record for James https://registers.nli.ie/registers/vtls000635132#page/130/mode/1up