Chili,
Another thing to consider is how you are going to attach the rear rack. If you have a vintage Pletscher, then no problem, otherwise, there are no braze ons on the seat stays of an old Grand Prix for attaching a carrier. The P-clamps that are readily available at hardware stores, suffer from metal fatigue and break even when you don't carry a load. That was an issue with my Motobecane. I finally solved the problem by making a clamp out of aluminum bar stock. It is a simple solution, but a bit too complicated to describe. I will take some pictures in the morning when there is enough light in the garage for the camera to focus.