Paging Dr. FABO: Need help diagnosing a 318 stalling problem

Has the fuel tank ever been removed and flushed? People take that for granted. These cars are getting close to 50 years old. All kinda crap is in the bottom of the tank for the pickup to suck up and get into the entire fuel system. If it has not been flushed, remove the tank, flush it, disconnect the line at the pump and carburetor and blow it out GOOD. Put a new filter on it and put it back together. Until you get that ruled OUT, you're lost.