I had a similar problem with my late 74 260 with the flat tops. A friend and me swapped out the carbs and mine started right back up. When you ran out of gas you sucked air through the power valves which have little diaphragms inside. And when u sucked air through them you blew the diaphragm. Have your carbs rebuilt.

After I replaced everything from the gas tank to the fuel pump, fuel filter, all fuel lines, all fuel injectors, etc....I had to fill up my newly refurbished/cleaned/sealed gas tank for the first time. Well the engine just turned over and over and over, and I was very bummed out. A mechanic friend told me to unscrew the gas cap. As soon as I did that it STARTED immediately and I went off on my first test drive! There was something about a vacuum or pressure that was keeping the fuel from being able to flow through the system this first time. Once I did that, the car started, and has ever since....100's of times