The Cargo stand ramps at KSDF don't require to support specific airplane types.
They can work with any cargo airplane with a Main Cargo door on the front. But of course, the airplane itself must be configured properly for GSX, and the Captain-Sim 737-200F is not already included in the GSX internal database, which means you must create a configuration for it before being able to use it with GSX, at any airport.
Also, be sure the AFCAD in use is the one that comes with GSX, by checking the parking customization page because, from your screenshot, it seems as if GSX didn't recognized the airplane was inside a parking, which might happen in case of an AFCAD conflict.