Graupner radios are really rare there are very few people use them with ardupilot so there really arent many people that can help you unfortunatly. Last time i set one up was over 4 years ago
I never said it doesnt work, just that there are so few people using them that you will struggle to find somone to help you.
If your still stuck, this is the converter i used last time I had to use a graupner radio with Ardupilot just set the port for mavlink 1 and it should work.