Thanks for your detailed note on the Guinan name. My mother was a Guinan and her ancestors arrived in the Philadelphia area in the mid 1800's - probably during the potato famine exodus. None of them had any idea about the origin of the name.
During a trip to Ireland some years back we also looked in the national telephone directory and were surprised at how few Guinans we saw. When I came across Ollie Guinan's name on a math paper I wrote and asked him about the name, and his reply was the previous posting. I don't know him or his background, so cannot vouch for his story.
Your researching sounds very thorough. Please keep us informed as you learn more.