The Stovebolt Site Forums The Parking Lot Big Bolts Disc brakes for 1.5, and 2 ton trucks

Look at this PICTURE
It shows both the 5/10 lug and the 8 lug axle.

The P30 with the 5 lug front axle has a 10 lug rear axle, very same way many of these old GM truck do.
So the wheels have 10 lug holes and fit front or rear, just the front hubs have only 5 studs.

I would not pick an axle based solely on the wheel size fit to it. They also made 8 lug 19.5 wheels.

I think if you have a 59 GMC 2 ton then you have 6 lug Budd wheels. The bolt pattern you get with this swap is 10 lug on 7.25" bolt circle with 5.25" center hole, hub piloted. Most common wheel by far is a 19.5". Some 22.5" wheels exist from the later 50's and only used on some Chevy 1.5 tons.