Well if they’re going for the “Ol’ Reliable” of Irish steam, surely it would be the J15; then again, and as @DoctorPan says, the WTs have a lot in common with the LMS/BR Tanks, and making a whole range of them for both IRM and Accurascale might work, especially with their high concentration in both countries. Revisiting the whole idea of a IRM-Accurascale range, the GSR Moguls/SECR N Class might be a good choice. I wouldn’t be surprised if it was a GNRI 4-4-0 or a B1a, though.