When you say "sedan converters" do you mean 12mm hex adapters? I have a set made by DrivenProductions made of delrin and they work great. Not sure what you would do for the front of a GB02 though, maybe the wheels would just bolt up with no hex. I've been running 1/10 touring car wheels/tires on my GB01 in parking lots and at the skate park for a while now.
You can also get 12mm adapters from a parts tree from the GT01, the 1/12 tamtech touring cars. That is if you can find it, it as with other tamtech parts have dropped out of most US stores. RCMart still carries them I think.