Hi Col
I am not at all familiar with the development of Newcastle so may not be the best person to ask about Walliers yard.
Looking for old maps of Newcastle brought up
http://www.tomorrows-history.com/mapping/maps.htmThe oldest map showing the Forth banks area was the 1894-1899 map - the earlier 1856-1865 is sadly blank North of the Tyne. The 1890s map shows Forth Banks and Forth Street but is missing Forth terrace where Robert Mains dwelt in 1851.
The description of the 1851 enumeration district (St Nicholas, 2e) describes it as "All that part of the Parish of St Nicholas comprising East side of Forth Banks, Regent Street and Forth Terrace as far as the corner of Forth street. (added in a different hand) down to Hawthorns stairs.
I did wonder if some of he Forth addresses were pulled down to make way fro the railway station but according to Wikipedia this ran from 1845 to 1850 when the Central Station opened. So that did not explain the missing streets.
I have looked in
http://www.historicaldirectories.org/hd/for a Directory close to the enumeration date and found Wards 1850 Directory of Northumberland and Durham. This includes a guide to the streets of Newcastle. (From the home screen select find by location, select Northumberland, select page 2 of the list and click Directory at the right hand end of the Wards 1850s title line. When the frontispiece comes up click browse directory and then go to image 133, which should put you in the middle of the street directory and then go to next or previous as you wish. The site is tediously slow at the moment so you will need patience.) The street directory includes the following
Forth banks, west end of the Close to Cattle Market
Forth row, Forth banks
Forth street, head of the Postern
Forth terrace, Forth street
Postern, foot of Westgate street to Forth street
Regent street, Forth terrace
Forth banks runs from the Close to the cattle market, passing the west end of the Central Station, and its route is more or less unchanged up to modern times. Forth terrace and Regent street were listed in the Directory as parts of Forth street, which is the modern street running along the south side of the station. The old city walls ran up behind Orchard street and so probably East of Orchard street was the Postern (signifying the former presence of a gate in the wall). This means that in 1851 Robert Mains was living just South of the Central Station. Wards 1850 Directory lists quite a few yards in the street directory but unfortunately not Walliers high yard.
There are some pictures of Newcastle Central Station at
http://www.newcastle-arts-centre.co.uk/Exhibition__Preview.htmForth street can be seen on the left of the 1962 picture of the station from the roof of the keep and also on the right of the 1972 aerial view. It looks as if the housing had been bulldozed by 1972 since the space seems to be mainly car-parking.
All the best
Gobbo