There are a bunch of Ford part supply houses, one that has Econoline king pins is http://macsautoparts.com/
our napa keeps them on the shelf. o riellys shows them (youll need a experenced counterman who can read a book not just a computer)
the moog book lists econoline 61-67 with two listings for king pins, 61-63 P/N 8470b with pin size of .7410" x 6.220" 64-67 P/N 8485b with pin size of .7410" x 4.910" I am a parts guy. Hope that helps