In order to have disc brakes front and rear on the XR/CRF, you have to upgrade to a different swingarm, front fork assembly, and different wheels with disc brake mounts. it would probably be cheaper for you to pick up a second set of stock wheels and put street tires on those wheels, it then becomes a 15 minute wheel swap.
Here's an older pic of one of my bikes, it has XR70 front forks on it, and IRC MB38 scooter tires.
Here's an older pic of one of my bikes, it has XR70 front forks on it, and IRC MB38 scooter tires.
