Hi,
in Germany the regulations allow any modificiation which was available within the first ten years after the car was built. So for a car built in 1980 you can install anything which was availabel till 1990, newer parts will most likely sacrifice the "H"-status.
So, yes, a turbo is an option I am thinking about but not now. Too much money already went into that project and another EUR 5k or so is not affordable at the moment.
And of course thank you very much for your kind comments.