1969 dart alternator problems

i have a 1969 dart . i think the alternator is stock . the car has a new blue holley electric fuel pump on it and is wired in properly. i dont think the alternator is putting out enough amps to run it at a low idle , i have to idle car high to give the pump more amps so it will not stall at idle . what is the stock amps and what size alt can i get in a bolt in package as i dont want to mod any brackets .any help would be helpful