I have traced my ancestry on this side of my family safely back to the above William Dillwyn who was born in Philadelphia in 1743. By all accounts he was influential in the Quaker movement and moved back to the UK to be married in 1777. "My" part of the family moved back to Wales within a generation.
The information I am after is more detail on his ancestry and thus any of the following people:
His parents were John (no dates, died in Philadelphia) and Susan (nee Painter) (d ?1785 Philadelphia). After Susan's death, John also married Mercy Pearce.
His parents were William, who I understand fled to the US with William Penn to escape religious persecution, and Sarah (nee Fuller)