It would be best to end capaill with a slender L, to clearly distinguish it from the broad L of capall.
Thanks. I have a pronouncing guide and it says that "ai" can be pronounced either "ah, aye, or a (as in fat or mat)" What part of this word makes the ai as short i sound?
It’s the final -ll that does so in this plural word. (In older books, final -ll was one of a class of phonemes called “protected liquids” which could affect the usual pronunciations.)