Well . . . . That does make sense.
If the front propshaft driveshaft bearings have gone to that extent the chain will be slack and able to jump about on the sprockets.
The chain drives a sprocket on a short shaft with two bearings on it. The flange that turns the propshaft is on the outside of that. There are high radial forces at play here.
I suspect the oil seal in behind the drive flange has also failed and you have probably lost all the oil from the Transfer Box -
HAVE YOU NOTICED AN OIL LEAK ?.
The fact that it has developed so fast makes me say
"DON'T DRIVE IT". The chain will be constantly turning and will thrash the shaft to death - probably ruining the Transfer Box casing in the process.
Removing the front propshaft will reduce the load on the chain and shaft, but won't stop it thrashing about.
If it has lost its oil, and it continues to leak when topped up, don't use it. There is an oil pump in there that keeps the bearings lubed and if it runs dry everything will wear rapidly.
So, what to do next . . . . . .

.
You need to have a working Transfer Box fitted before you do any more miles.
I have a Transfer Box for an Auto, but its untested, I intended to re-build it over the winter. I don't carry many spares for them so if I started now it would be a couple of weeks at best before it was ready. Midhurst is also the best part of 1,000 mile round trip for me (with a fuel shortage). We need to find someone closer !
Karl Webster breaks Landcruisers, I wonder if he has one, I'll see if I can contact him.
The big question is . . . For how long can you live without the truck ?????
I'll see if I can rally the troops

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Bob.