1964 C10 suddenly running terrible

[62gmc910]

I have been troubleshooting old machines for a long time and most people want to blame the carb and fuel. carbs do three things run lean run right run rich. Lean is usually cut out or jerking, rich is lower power black smoke and flooding. Ignition is more often sporadic and sputtery. if the truck runs ok then quits chances are its ignition. CHECK for spark when it won't run if the spark is other than Blue or blue white it probably won't fire under pressure
if it is orange the coil is suspect
Plug wires for modern electronic ignition don't work well with points
have you checked the point gap , it could be marginal and go out of range when the engine warms up