I would agree with doing it yourself or finding a local alternator rebuild shop to do the motors for you. You probably will be better off taking them the weakest one and get a quote if you don’t want to attempt it yourself. Somebody in your area knows the GUY that does starters and alternators. You may have fewer issues than you think. If you have a 67-9 Camaro that has smooth functioning rear windows,power or manual,it is because someone totally dissembled them,lubed the tracks,replaced any broken pieces and adjusted. Only a low mileage original car would possibly escape this procedure. You will definitely be removing the rear seat and panels if they are assembled currently. Good luck….more time than dollars on that project.