If it helps at all, I put a little video on Youtube demonstrating how to check an early Ford axle ratio.
Bear two things in mind: You turn the free hub or wheel twice, and the other hub stays still.
https://www.youtube.com/watch?v=bkvp3Fq21ZM
You can also hear my English Birmingham accent - think of Ozzy Osborne without so much slurring.
It might be, as it is a truck and may occasionally be expected to carry something that a 15/29 gaerset in the trans might be more suitable especially if used with a 3.54 rear end, and still worth considering with a 3.78.
Mart.