I have been looking at both deeds and tax lists as well as wills & estates from (mostly) Chester County, Pennsylvania. I have not seen William Paschal Alexander - or if I have I'm not remembering the name. I am also talking about fairly early - between 1720 and 1778.
In 1778 my ancestor, James Alexander, left Pennsylvania for North Carolina.
However, I should think that the name 'Paschal' should give you some good clues as to his origins. It's not a very common surname - perhaps it was his mothers or one of his grandmother's name. If you find a bunch of Paschals somewhere in Pennsylvania, you might be able to find your William's family. . . . . just a thought.