Thank you for the Porterfield in County Donegal information. . . . . let's just hope that Frank Burke Porterfield knew what he was talking about! That his information is well-founded. Without the documentation there is no proof.
I guess the next thing to do is to begin checking out all Presbyterian records in County Donegal. I don't think they are particularly plentiful for the time period that we are interested, but we can give it a try.