I know little about Ford trucks. Back when I was a truck mechanic I serviced a fleet of big Fords, but that ended in 1981 and I've not stayed in touch with Fords since.
80 inches seems a lot more like what I'd expect.
Are you committed to a straight axle setup? I have a Chevy P30 that is about 80 inches across the front tire. Its an IFS and I assume could be adapted to a Ford frame similar to the way Chevy pickup IFS can be adapted to an AD Chevy.
Just a thought.