Ok I have the moparts Tech chart, but its not clear to me for whatever reason on what driveshaft length I need. I have nothing to go off of and my drivetrain is out. Its a 383 , 4 speed 70 roadrunner with 8 3/4 rear end. Im guessing I need the 53 1/2 length? Or will a 51 1/2 one that I have work? Just someone out there tell me what I need so I can get this thing made up. Im tired of going over that chart. Thanks guys!