It would not surprise me if you mistook the AIB/Provincial Bank note as being it, because to this day, they are more Irish in appearance than any other currency in the country, and were more Irish in design, tradition and style than even their Southern counterparts.
With a bit of messing around, we can speculate on its appearance.
First, all the series B notes featured a calligraphic background.
Second, it would have a small face full length portrait. the Carolan 50 gives a clue.
Third, the rear, maps and sailing ships.
Colour. It will have to contrast to the 50 to avoid confusion. It won't be Red, likely Turquoise.
I'll get a new laptop and spend a few hours working out the design. If anything it will be relaxing.