How are vowel sounds with acute accents written now that acute accents aren't used in Gaelic?

[Polygot2017]

I've been learning the pronunciation of the Gaelic letters/sounds, and I've seen that the acute accent used to be used on the letters 'e' and 'o' (and sometimes on 'a' or presumably other vowels to differentiate between unclear and clear vowels). I've also noted that the acute accent is now no longer used, only the grave accent. So my question is: how are the sounds that were previously represented by the acute accent now written?

[GunChleoc]

They are written with a grave accent.

[Polygot2017]

They are written with a grave accent.

Ok. The thing is, the letter 'e' with a grave accent is pronounced like 'ay' in the word 'say', whereas with a grave accent it's pronounced more like 'ai' in the word 'fair'. Similarly, the letter 'o' with an acute accent is pronounced like 'owe', whereas with a grave accent it's pronounced 'au' like in the word 'caught'. So if Gaelic now uses grave accents in place of the old acute accents, how would you be able to tell which form of 'e' or 'o' is being used?

[akerbeltz]

Um I won't go into the "sounds like" because those sounds are seriously variable between English speakers é is /eː/, è is /ɛ:/ (open eh, i.e. open your mouth more), ó is /o:/ and ò is /ɔ:/ (open oh, i.e. open your mouth more).
You have to know which is which but that's worse that it sounds. /ɛ:/ and /o:/ are quite rare, probably less than 20 common words have either. So basically, once you know which words used to have ó and è, then assuming everything else is /ɔ:/ and /e:/. There's a list in Blas na Gàidhlig somewhere, I forget which page.