I was going to say fuel system problem. A low tank with a crud filled filter, cracked pickup tube/clogged sock, and a fuel pump that has poor action because of age, will drive you crazy. When you go uphill (or on the side of a high crown road), the system may not get enough fuel to the carb.
First, I would try the inlet filter to the carb, then go backwards. Any suspicious clean streaks near the fuel line could show a leak. Sometimes, these leaks only happen when the crud in there is jostled inside the fuel line, it can plug up a crack. You could easily have a completely stock system and many things can happen in 40 years, especially if it was sitting for almost a year. I would also check for rust in the tank.