Renault's approach to this is that "new style" doors will fit old style bodies. In fact a friend just had it done on his R4. After studying my Jogging (new style) we found that there was no major difference on the A- and B-posts, so he discussed it with his bodyworker, who was very reluctant initially. But finally he managed to get him to fit them.
New style hinges have two M6 studs welded on, so there are no nut blocks needed. I think there is a reinforcement plate welded on the body (but I may be wrong). n any case, a rectangular steel plate, say 2mm thick, sandwiched between the nuts and body pillar, would make a perfect job of spreading the load.
To actually fit the door you need to cut the old hinges from the body and measure carefully where to drill. The best way would be to hold the door on place while you mark the hinge stud position. This does not need to be dead accurate as the holes are to be drilled oversize anyway to allow door adjustment. For the rear doors, as you will have no access to the hinge nuts from the inside, you must cut two oblong shaped windows on the inside of the B-pillar.
Bertl, I don't think it's worth just putting new hinges on an early door. Malcolm was right saying that you have no access to weld them, furthermore the door skin contours are different on each door, the old style ones have a cutout for the hinge which must be closed somehow. Better find new style doors, there must be plenty of them in your country, as they come from later cars they should be in better shape and as a bonus have always the plastic window frames.
I will have you some photos of old vs new stule doors tomorrow.