I am also looking to find proof of William's Quaker heritage. My sister, who is a Quaker, said there is a library in England that is not online where all the Quaker records are kept. I do not live in England so I don't know how else to find the information. He must have been Quaker though because all down the line the Plasketts married Quaker women and were not disavowed for marrying out of unity. Please feel free to email me and we can share more information as we find it. I have Hinshaws Quaker encyclopedia on CD and it has helped me alot on the US Quakers.