Standard 3600 would be a 4.56 rear axle ratio (mine was), but I bleieve there was an optional rear end that was even higher numerical ratio (5.??) that he may have.
Regardless the tire size has a significant influence so it will be helpful to hear what he actually has.
Correct, in 1949 there was an "RPO 3600" that had 5.14 ratio rear axle gears.
Here's a page from the 1949 Vehicle Info Kit with that stuff highlighted. It's possible that people referred to the 5.14 ratio as "Farm Gears".
It should be a fairly simple swap to the more common 4.56 gears.
