Your welcome Munch,
I haven't found Shiel's Yard, Dundalk but I did find Shiel's Court and this was just off Bridge Street where it runs into Church Street, and Shiel's Court is now called Patrick's Street. I think Shiel's Court may have originally been the entrance lane to Shiel's Yard, or maybe Shiel's Court was also known as Shiel's Yard.
You can look it up on the 1854 Griffith's Valuation map of Dundalk on
http://www.askaboutireland.ie/griffith-valuation/ and do a search for any surname in Dundalk and open the map in the middle of the town of Dundalk. You will see Sheil's Court is east off Bridge Street which runs from the bridge over the Castletown River in the north of Dundalk and runs south down into Church Street.
Gallowshill is also on this map and if you follow Church Street south down to Clanbrassil Street, down Earl Street, south east down Park Street and Anne Street, east into Dominick Place and then Gallowshill which continues as the Carrickmacross Road. On this map Gallowshill is just to the west of the Ard Easmuinn junction with the R178 Carrickmacross Road.
I hope this helps.
Regards, McShane01.