Test for low fuel delivery on a carb truck:

Take off the air cleaner and hold the choke open and work the throttle repeatedly, counting the cycles, until the accel jet squirter quits squirting. You've just flooded it, so let it sit a while and clear out. Take it out on the road, and accelerate as hard as you can until it starts to bog out, and quickly kill the engine and put it in neutral, and coast it to a stop. Remember the p/s and p/b will be gone, so be careful. Without cranking the motor, repeat the cycle throttle and count squirts test. If the count is less, fuel delivery is inadequate. If the same or very close, delivery is fine.

Have you had the head off? I sort of suspect cam timing if the ignition timing checks out. You should be timing it 7* BEFORE top dead center, to the left of the T mark.