I think that there is no question that you will have to either rebuild or replace the wheel and master cylinder and brake hoses.
You can inspect the drums and lining. The original setup worked fine for many years. I drove single brakes for many years when thats all we had and I still have them on all of my old jalopies. However, if the single system worries you, I would replace it. A person must have confidence in his brakes. You can get kits that mount under the cab like your original master cylinder. Its easier than trying to fabricate linkage for a firewall mount. Once you get it running and stopping good, you can decide how much body work you want to do.
