Sorry for your loss. This must be a difficult time. I'm sure you will feel some relief on the financial side when you get the tax issue resolved.
As far as I know, Revenue will accomodate a deferred payment schedule, but will charge interest on the deferred payments. So you would probably be better off getting a loan yourself at a competitive rate to pay Revenue, and then repay the loan yourself.
I really don't see any relationship with Eircom shares to be honest. O'Reilly & co did a smart business deal - they bought at a low price and will sell at a higher price. Given that Eircom investors lost about 1/3rd of their money in the deal, you might still be able to use the remaining the 2/3rds repay the tax man.