It really just comes down to your budget. I would look at upgrading the front forks to a set that has a disc brake bracket, and running a cable pulled hydraulic front disc wheel setup with the rear staying as a rim brake.
Cheapest is to just get new wheels in 650b with drum brakes so that I can keep the fork and not have a franken bike, which is still a pretty penny for what is basically a toy.
I like the idea of a weather proof non motorized bike build using an aluminum fixie frame for sporty handling and using smaller wheels so I can have full fenders. So it wouldn't be a complete loss if I decide I don't like shifter bikes either.
I disassembled my motorized bike because I didn't enjoy riding a single speed motorcycle. I wrote before that the 50cc engine did very well, and I still believe that but no matter the power I will always be disappoint with only one speed.
I do believe this chicago schwinn frame with the drum brakes and a 3 speed hub would look great and do what I want: cruise around 20mph with adequate braking and keep the engine at peak torque at a variety of grades.