Poser, I always appreciate your prompt responses! Do you know how much wear is acceptable? For example, I am rebuilding a case because my current one will pop out of lo-range on hard decel. I inspected my donor case, and the lo range gear as well as the coupler look very good. There is some wear on the fork, but not horrible. There is about .022 between the edge of the fork and the coupler. Not sure if there is a spec on this, but figured if anybody would know it would be you! Thanks again.
Something had to cause the fork to get worn like that. There is a fair amount of ambiguity inherent in the original one-piece Land Cruiser transfer case.
When you assemble your case, make sure that your range selection fork centers on the shift collar, and that these pieces center on the main shaft and gear assembly when the fork is moved between the detents on the shift rail.
Something else you want to pay attention to is the amount of wiggle/wobble that the high and low speed gear has on the main shaft, between the thrust washer and main shaft bearings. If these gears are allowed to move fore and aft on the main shaft between the thrusts and the bearings, it could cause the case to pop out of gear like you were experiencing.
Shifter linkage clearance between the body tub is something else you need to look at. If the engine/drive train can flex because of a worn or shot engine mount it will allow the assembly to shift and can cause the shifter lever to hit the body tub and knock the case out of gear.