I have checked the newspapers and found nothing, which surprises me as I have been very lucky with other newspaper searches when it comes to court cases. People did like to read the court news to see who was in trouble for what! I have Google Nash v. Callaghan and found nothing, it must have been a minor case. I did a search of the Registry of Deeds and found a deed from 181 between William Nash and Daniel Callaghan, but it appears to be a land deal, I have to read it through more carefully.
Thanks for the suggestions, but I fear any traces of this court case and the will that started it are long gone in the fire of 1922.