I think that I would verify the cam setting first,then if that don't do the trick then I would go to the carb next and make sure it is in top notch shape with that said make sure the carb power valve is not blown if one is used in that carb also the it might be the idle air bleeds are not right for that motor, where are the idle air screws set at and do they make a difference when you screw them in or out there are a lot of little things that can cause it to not run right, is the motor rich at just idle or all the way thru the rpm range,i worked on a buddys 440 roadrunner for days, and he had the same problem but the car would die when you put it in gear only to find out that he had a cam with a lot of duration and was trying to use it with a stock torque converter