Gerhard's photo is an excellent depiction of a hub flip. What makes this work is that the bolt pattern in each end of the hub is identical - i.e., the axle drive flange bolt pattern to the hub is exactly the same as the brake drum (technically, brake drum extension) bolt pattern to the hub, so the hub doesn't care which way it is mounted, as long as the wheel studs are in the correct direction.
In the single configuration as shown, the wheel mounting flange is to the outboard side with the wheel studs as pictured. In a dual configuration the wheel mounting flange is on the inboard side against the brake drum extension and the direction of the wheel studs are reversed relative to the flange so they are again pointing outboard.
As a matter of fact, the front axle and rear axle hubs are the SAME part number (#1089670
, just mounted in opposite directions, so I suppose if you wanted you COULD flip the front hubs and run duals on the front. I doubt you could turn the front wheels enough to be able to steer very well, if the duals would even fit within the wheel wells.
By the way, the wheel bearing cups are the same inner and outer so you do not have to reverse them in the hub. The wheel bearing cones (the races) are different, the inners have a slightly larger ID, so when you flip hubs the inner races have to remain on the inside and the outer on the outside. Also, DO NOT forget to replace the small cork seals in the lock washer keyway, if you don't differential oil will find its way into the hub, leak out through the seals, make a general mess and will probably ruin your wheel bearings also!