I had to do some math for this, just for fun, not to bash anybody.
First of all, axles only hold the weight of the chassis, drivetrain, and body, so axles and wheels don't affect bearings throught their weight alone, only by their supporting position.
With that in mind... Here's the scoop.
Force (weight in this case) multiplied by distance from pivot (pumpkin in this case since both spring forces can be added into a single force over the center of the axle) equals torque. The torque put on the axle by the weight on the wheel is therefore equal to the torque put on the axle by the weight on the bearing. Newtons equal and opposite law.
That means the bearing force on the axle multiplied by its distance from the pumpkin is equal to the wheel force on the axle multiplied by its distance from the pumpkin (WMS/2).
Given that info with a narrow trac amc 20 and some exaggerated assumptions, a 1" wheel spacer will add 79 lbs of force to the bearing or the equivalent of a full 20 gal fuel tank plus a few lbs vs an empty 20 gal tank. (Fuel = 7.29lbs/gal)
And that's IF a CJ put 1000lbs on a rear wheel and the bearing was 6.5" from the WMS.