Well I tried harder and could detach the dog bone from the swing arm.

Then, with some effort, i could get the relay arm and the shock inline. The relay arm was free to rotate, but it was tight around the "clevis" of the shock (or the other way around)

Then i found a swing arm position which was ok to align with the dog bone, just as Pleiades said. Thanks a bunch.

The good news is the few spacer/screw i got out where almost clean with a thin layer of grease on them, although there was a 5mm thick layer of chaine lube+dirt everywhere outside.

I rode to the sea for a relaxing test ride and no problem. New cush drive rubbers (fitted with old tube rubber as suggested on the forum) really makes a difference.