Then there's this word - ionnán - is it another form of ann ?

- má tá tu ionnán run do chongbháil - translated as - if you are able to keep a secret, but word for word : if are you (in yourself) a secret your keeping.

Modern standard version: 'má tá tú in ann rún a choinneáil'. 'Bheith in ann' is a very common idiomatic phrase meaning ''to be able'. Check it out in FGB.

Go raibh maith agat

Yes I do recognise that idiomatic expression, but I didn't understand the exact meaning of - ionnán - again it's not in Dinneen.

Probably no one understands this phrase literally.
That's why there are many different spellings from i ndon to ionnán.

This story begins like this - A bhfad ó shin - is this a dialect form of - I bhfad....?
The next line is - bhí fear d'ar' bh' ainm Páidín O'Ceallaigh - of course today this would be written - darbh, but as it has been taken apart here, why is there an apostrophe after - ar - and - bh ?

There’s no comma but an apostroph.

do a ro bha -> d'ar'bh' -> darbh

do = to
a = relative pronoun
ro = perfect particle which only survived as -r.
ba = past tense of copula, lenited because of ro

Go raibh maith agat
I felt certain that those apostrophes were hiding something there- it was the - ro - that I didn't know anything about. When I looked it up in the Teanglann dictionanary, I got the impression that the copula in the middle of it all was - ar - which is why I was wondering what - b(h)a - would be doing there, coming just after it.

Here are a couple of questions I have. In this text the word for a queen is spelt - bainríoghan, for example : - Tháinig rígh agus bainríoghan na sídh 'nna láthair agus dubhairt siad : ....srl
But a bit further on in the text there's this - Bhí capaill réidh ag gach aon aca, agus an Cóiste Bodhar le h-aghaidh an rígh agus na bainríoghna. Am I right in thinking that there's a mistake there and that perhaps those last two letters should be the other way round ? And the Cóiste Bodhar ? Is it called that because it makes a lot of noise or pehaps could it mean that it's silent ? deafening or deaf - .i. silent ?

'Bainríoghna' = genitive form of 'bainríoghan' (modern spelling: 'banríon; banríona'). FGB: 'cóiste bodhar' = 'headless coach, ghostly funeral hearse'.

Go raibh maith agat