firstly the clonk. As you have found there are many places where the clonk could lurk.
UJ's - 6 off
Drive shaft splies - 2 off
Propshaft spline - 1 off
Diff support pins = 4 off
Damper drop arm
Damper attachment - lever arm
Damper attachment - strut. top/bottom
Dampers and struts could produce an internal knocking but not common.
Diff input pinion
Diff front support cracking
Diff output pinion keyway - 2 off
generally UJ's and the splines show as wear. If there is any that you can feel then there is more that the engine can extract - so change them
The diff mounts are easy to feel and see
The diff itself always has some play in it. This could be the problem but leave till last option.
The hubs do not generally produce a knocking sound. Bearings grumble and can be easily felt.
As for the hub. As mentioned by Mickey the hubs are 40/50 years old and their history could be very chequered.
If they have been laid up in a barn for 30 of the 50 years then you could be on a good bet. If there is any doubt then I would have them changed.
They do fail and it is suddenly whilst on the move.
A number of people have changed over to CV shafts but this simply swaps one issue for another. Good NEW hubs will work safely for many years
I also have a 'take-up clonk' and am doing all the same things as yourself. I'm beginning to think it may be the newly serviced diff