Replace freewheel with freehub? I have a Motobecane Super Mirage that I bought in 1977. I have another bike for regular use, and I've decided to completely rebuild the older one. I determined today that the freewheel teeth are worn down, so I need to replace that. I am just learning about freehubs. Can I replace the freewheel with a freehub setup? What factors do I need to keep in mind if doing so? 

Thanks
You'd need to replace the hub (i.e. build the wheel with a new hub -- typically, its better to just get a new wheel), and then respace the frame (i.e. coldset) to take the new hub. 

It's easy still to find freewheels, so I'd recommend you just replace the freewheel.