Any 3/4 ton differential gear set from 1946-1972 will interchange with your friend's 5.14:1 without too much dinking around.
Most 3/4 tons came with 4.55:1 but a few came with 4.10:1 or 3.90:1. (mostly the automatics)
Just keep in mind that that truck is geared like it is to get your one ton of cargo moving. If he's planning on using the truck as a truck, he'd probably be better off with the 5.14 gears. (He could probably get away with the 4.55 ratio, too.)
Also remember if you make it go faster than the brakes are designed to stop, you could be in trouble.
