I have done such a conversion on an OROV 2.8 Chassis.
Check out my build guide here
I would contact Rusty to see if he has any of the M100 motor adapters left.
You are going to have to be a real DIYer as this is not an easy conversion.
I still have yet to ballast the converted chassis as the three M100 motors add around 225 gms to the rear of the chassis.
Other forum members have done such a conversion so do a search here for additional input.