Not just the wagons, but the whole layout... that's as good as it gets-ever! Absolutely TOP class stuff, every detail... track, ballast, models, paint jobs including weathering. A real work of art as well as railway modelling.
With regard to the sizes of the wagons, I doubt they would have used an exact copy of GNR ones - though quite possibly at times Dundalk might have built or repaired wagons from this line. Therefore, I would be more inclined to believe in different sizes being prevalent, rather than uniformity.
From recollection, pictures showing "H" vans in SLNCR train consists indicate that they at least were marginally larger. The GNR vans would have been closer to "H" vans in dimensions, therefore smaller SLNCR wagons was probably the norm.
Bear in mind also, the SLNCR hadn't a brass cent to its name. Thus, while the GN and CIE were upgrading with (inevitably slightly larger) wagons in the 1940s and 50s, the SLNCR was more likely just patching up older ones of their own.
jhb171-Senior remembers noticing how down-at-heel most SLNCR wagons seemed to appear when he saw them in cattle trains at various locations on the Irish North.