Hello Deickmeyer and thank you for your question.
The John Deere 54 in. Bagger for Tractors (Model # BM21376)will not fit your GT245 Garden Tractor.
The John Deere GT 245 with a 54” deck requires a Bushel Hopper Assembly (Part Number BM18675) and a Rear Bagger Chute that can be obtained through your local authorized dealer. This link will help you locate your nearest dealer: http://dealerlocator.deere.com/serv...
Best wishes on your project.