It wasn't really limited to rural Ireland. MPH was on all speed limit signs and was because all vehicles were imported from the UK where MPH were and still are standard and the entire Irish fleet didn't yet have dual speed markings on the speedometer. Once they did then the signage was exchange countrywide within weeks, if I remember correctly. Distance signs were changed slowly over a longer period as it wasn't so critical to the safety of driving.

Stones and feet for people's weight it still used in common parlance, again not limited to rural Ireland. This is just the inertia of tradition. Doctors and such professionals would always use metric now of course.

With the exception of pints of beer which is still the standard today, food and groceries were already metric in the 90s. Source: I grew up in rural Ireland ;)