Thanks for the input guys !
A month ago I went to see a guy who has been balancing engines for at least thirty years now. He has been balancing everything up to top fuel engines, so I believe he is the guy to do the job.
He had a Citroén 7C convertible project sitting in the shop. I think he said it was one of only two known of the first modelyear still in Europe. He travelled through France in the seventies picking up NOS parts for the restoration, but it´s still sitting there.
Finished it will look something like this, that I found when I Googled Citroen 7C:
