you can use part number GCEXXL (the 6.2 cu ft) or the GCEX (the 4.15 cu ft). List is 329.00 for the GCEX and 459.00 for the jumbo. We do have a dust cover for both. The part number is GCDust or GCDustXL. They come in 4 parts and attach to the outside of the bagger using small machine screws. Cost is 50-65 bucks depending on the dealer and what size you need.
Since you have an ultra cut deck, I would reccomend you get the 2004 model Accelerator. The distributor in Michigan (PACE) just got a bunch of these in, both in the Jumbo and regular sizes. The opening is 3/8 inch taller to optimize the fit on the Ultra cut but still retain the fit on the other exmark decks. The box is marked "Extender Ready". Ask your dealer to have pace send a unit with this marking and the performance will be slightly better than with the 2003 model catcher.