Ernst; I have a reference at home that may help. In the meantime I have found this link
http://search.ebay.com/1968-442_W0QQ...rvZ1QQsbrsrtZd
to help you a little. These are just a quick "window" look at prices here in USA and most are not complete yet so may bring more.
It sounds like your car might be a high 3 or perhaps a low 2 condition car, would you agree? I will check my reference soon and let you know what it reads. And, welcome to our site.