Thanks dudes, but got another trouble here.
We have two typical dynamometric wrench which seems to be useless here because the shock shaft itself turns together with the nut. I mean, yes ok, the bush gets compressed, but there is kinda no torque limit.
So i guess a special "lateral" dynamometric wrench is needed so that the shaft can be stopped / blocked at the upper end from turning fool whilst the nut is tightened from below ??
Otherwise I can't imagine another way to do this job. Perhaps just tighten both sides, measuring the visible thread length to get both sides matched??? But in this case it would just by naked eye, without torque settings.