You can make them work. You just need to be sure that you are jetted properly. If they're the Kadron Solex 40's, they'll have the 28mm Venturi in them. If they're used, just be sure the bowls are good and clean, and the throttle shafts are tight. If you need to rebuild them, take a look at the diagram on this site under tech articles.
http://www.german-pride.com/Joomla/index.php?option=com_content&task=view&id=25&Itemid=70It's got an exploded isometric drawing of the Kadron carburetor. Rebuild kits for the kads used to be cheap but are now $28.95 per carb.
http://www2.cip1.com/ProductDetails.asp?ProductCode=VWC%2D111%2D198%2D567%2DK&Click=10603I've rebuilt a couple sets myself and they are a VERY easy carb to work on/rebuild.
Good Luck with it!
Scott Faivre