In the book "Wills of Franklin County, Pennsylvania 1784-1826" it has:
p. 422 Apr.3, 1819, letters Admr. Est. of Wm. Duffield, granted to Simon Duffield & Sarah Duffield. Sureties: David Andrew & John Dickey.
p. 615 has Wm. Duffield mentioned as one of the sureties to John Rupp.
p. 39 James Duffield is listed as friend of Rebeckah Davis in her will.
In the 1830 census for Montgomery Twp, Franklin County, Pa., pg. 425, is William Duffield. I have this because he is living next door to John Rupe.
Hope this helps.
Charlie