One of my own memories of visiting my grandparents in Eire/the Republic/or as we still called it ‘the Free State’ was the age and condition of vehicles compared to NI. Back then there was no NCT (MoT in GBP) IIRC, so all kinds of things crawled the indifferent roads. If your layout is populated with 1950s British trucks in poor nick you’ll capture the look. There also needs to be an ancient tractor crouching somewhere. They seemed to be everywhere.
Now, if you were setting your layout in the 80s, you’d need at least one Hi-Ace van……;)