Brake booster replacement

Need some help, my son and I are working on his 72 scamp, 318 auto. Reading the threads tells me the brake booster is bad on his car (hard pedal/not much braking/air escaping) and looking at the booster we should be able to take the four bolts off the mount under the hood and disconnect the pedal in the same area and then take the master cylinder off and put the new booster on. Am I missing something?? Also, any idea where to get the booster, plus would you recommend replacing the master cylinder also?? Thanks for the help.