First off, you may want to post in the Classic & Vintage forum on this. AFAIK, Service Course simply means for road use, so it could be any of several models. Without photos and a description of the components, it's difficult to precisely identify the model. Also, French bikes of that era used French or Swiss threading and dimensions, so you need to take that fact into account when replacing parts such as bottom brackets. One factor in your favor for conversion to SS or FG is that the dropouts are horizontal and rear spacing is 120mm. As to the rust, you will to determine if it is surface rust, which is rarely a problem, or if it has rusted from the inside.