The Cannondale Black Lightning needs it's original derailleurs.
The bike came from the factory with special black and gold anodized Superbe Pro RDs and gold FD.
My brother still has the Black Lightning he bought new in the 80's and he loves the bike to this day. Only thing he was dissapointed in was the Dupont paint finish that chipped real easy. Otherwise he said that it's a nice stiff and light bike that climbs real good!
Maybe the original owner still have these derailleurs that you can buy from him??

Chombi
84 Peugeot PSV