Chuck's Trucks is a good source for parts if you can't find something locally.
Chucks Trucks LLC., Ford Truck Parts and Restoration, Chuck's Trucks, Chucks Trucks
When I had my '40 1 1/2 tons I was able to get all of the brake parts at my local independent store. I didn't ask about brake shoes. You probably have to have the ones you have relined. In regards to the wiring harness, if you are staying 6 volts make sure the harness you get will handle the higher amps of 6 volt systems. A good source in YnZ's in Redlands, CA.
YnZs Yesterdays Parts; Manufacturer of Classic and Antique Automotive Wiring Harnesses (ynzyesterdaysparts.com)
They will customize a harness to include turn signals or what ever else you might want. Not cheap but excellent quality.