OK. So it seems like you have the wrong knob on your high/N/low shifter.
Some more questions for clarification:
you show a differential in one of your pictures, and it looks like it has a cable locking mechansim. When you say you locked the hubs, are you locking the wheel hubs or locking the differential(s)? The wheel hubs are locked by turning the locking mechanism at the center of each front wheel.
In your post above, how are you telling that you are in 4wd or not? With the truck parked and the wheel hubs unlocked, you should be able to rotate the front drive shaft by hand when you are in 2wd. If now lock both wheel hubs, you should NOT be able to turn the front drive shaft. This tell you your wheel hubs are working. Next, unlock the wheel hubs and push the 4wd button (the engine should be running I suppose for the vacuum mechanism to work) to put it into 4wd, then the front drive shaft should lock up when you try to rotate it. If you can't get it into 4wd, then you need to inspect the vacuum shift mechanism.
FJ62 has a vacuum shift transfer case so there are thread with more detail about troubleshooting. Try searching. Vacuum lines could be switched at the valves mounted on the fire wall or the vacuum diaphragm could be broken. Or there could be an electrical failure.
You pretty much have to drive the truck to see if you are getting into low. You should be able to tell because you will be going about half the speed for a given gear/engine rpm as with high. If you can the transfer case into Neutral, then it should go into low too, If it won't come out of neutral, then inspect the linkage. If it goes into gear on both sides of neutral, then pretty much one must be high and the other low.
