Update:
I machined myself a rotor holder tool and successfully loosened the the screw of the starter clutch.
I also got myself a three jaw puller, but I still can't get it off!
I tried everything. Seventhreeseven: Where did you put each jaw to sucessfully get it off?

Is there any non genuine tool that also does the job?
I already bent that 3 jaw puller trying to get it off

try to do it russian way (optional step #1: get drunk), step #2: hit it by hammer. screw in the screw which holds rotor briefly, let it about one or two turns out from fully tighten to make place for rotor and hit it two to three times by hammer using something like brass stick or something similar. rotor might loosen.

I did something similar to what Ventyl is suggesting. I first got the bolt loose with a combination of heat on the bolt and then angry (Russian style) effort. Then I put the bolt back in loosely so the three-jaw puller had something to rest against. I put the jaws on the teeth of the wheel, if I remember correctly. Then I put some tension on the puller and started adding heat to the wheel, then a little more tension and more heat, then more tension and more heat, then it suddenly let go of the crankshaft with a loud pop.

I didn't bang on it with a hammer during this process but I can imagine that hitting it while it is under tension from the 3-jaw puller might help to make the wheel let go of the crankshaft.

Definitely. It is way how some tools for dismounting break drums work.

Update :D
So I went full German mode and just bought the special tool.
No matter what I did... that damn thing would not come off.
But with the special tool it was easy to take off.

Changed them... tried to start it for a couple of seconds without oil, an exhaust and coolant and the engine fired up (I put oil directly into each cylinder + there was enough oil for the pump to lubricate the camshaft).

YEP that thing fired up. So the combination works. I did not change the counterpart (the whole magnetic "pickup" thing).
I will add coolant and so on and check how good everything works.
Thanks mates :)

Good to hear it runs.

As I said a couple of days ago:

You'd end up with an interesting engine combination: '91-'92 engine that has the higher lift camshaft profile, and Germany restricted carbs, and '93 ignition timing. That combo would probably be a good sporty/lively setup (You'd just have to remember to do your valve adjustments to '91-'92 specification rather than to '93 spec).

And I understand that you're going to remove (grind off) the CV slide restrictors in the carb tops, so the engine will be even better.