the dual hubs are pretty light as it is. I have a set on our 9000 for the duals. Maybe have some machined from billet aluminum. Do they make aluminum rims this size?
How much weight are you trying to save? If you dont need the PTO you might be able to drop the PTO gears out to save weight. Would have to check if anything needs to be supported in there. I assume this is your pulling tractor?