I saw the pictures of bikes like yours in the gallery. I assume the tank is under the seat? Is it removable or is it integral (i.e. welded to the frame)? If its removable, your best bet is probably to see if anyone here can sell you one thats in OK shape. If not, you can buy a tank liner kit from a motorcycle place, or order it from like JC Whitney or someplace. They include an acid solution to eat the rust, some solvent to clean out the acid, and a liquid liner material to coat the inside of the tank. Needless to say this is all pretty nasty stuff. It will give you chemical burns in minutes if you are exposed to it and it takes the paint right off any metal it comes in contact with. It DOES work though. But, if you can buy a tank (or even a new frame) for cheap, that's the way to go.
You will probably need to clean the carb, regardless of whether the cable is broken or not.