The '75 Super Course was spec'd with the Nervar Sport crank, but many came equipped with the Stringlight 93 also. If the bottom bracket bearings are smooth I think replacing the cranks would be the easiest most practical route. You can usually find a set on ebay for $60-75.
On small rusted parts I use some chrime polish with a brass bristle parts cleaning brush. Gets rid of most of the rust.