I have a
b7500 with the RCK60-24b mower deck the grass catcher I use with it is the GC60B. I think that should work with your setup. There is a 2nd gearbox that is mounted over the right hand blade pulley and a driveshaft from there drives the mower deck mounted blower. The chute from there goes to the rear mounted bagger. The bagger mounts to a bracket that bolts around the tractor rear pto housing and the top link mount. The bagger doesn't raise and lower with the 3pth.
Here are some pictures:
IMG_0620 | Flickr - Photo Sharing!
Send me an email if you need more info or pictures