I have checked the engine number, but none of my books go back that far, the oldest book I have is a basic Auto Data Diesel volume 2, but it appears volume 1 which I don't have gives some data on those engines, which according to wikipedia was also used in Peugeot J5s around the same age.
The injector cleaning guide web page you gave does seem quite helpful if you followed it completely.
A pity you don't have access to an injector tester, you don't have an old tractor workshop or older commercial workshop or similar nearby as they often use them to overhaul injectors themselves. If you could see it giving a good spray pattern at the correct pressure, it could be eliminated as a a cause of your problem.
Where you say "I tried to switch injectors 2 and 3 and the problem oil on the injector moved with the injector." that would seem to indicate a dodgy injector.
When the engine is idling and noisy/rough does anything change as you open and close each injector union in turn?
If the fault still remains on one cylinder even after moving injectors along to a different cylinder, I would try and get a compression test and ideally a leak test also to confirm whether engine rebuild is required before further strip down.
Also when engine noisy at idle can you use something to act like a stethoscope to locate area of noise. Sometimes if careful a long screwdriver can do it.
Just a small point but are you sure when engine running, that both ends of each injector high pressure pipe is tightened correctly.
I expect you have checked the cam belt timing by now but the little circles and arrows on cam and injector pump pulleys are the correct original marks when lined up, I can't remember for sure but you may need to remove the four allen bolts and crankshaft pulley to see the timing marks on the bottom pulley, it was a long time ago I last saw some like those.
