I have a 68 convertible clone with a TH400 and a 2.56 open diff. I have found a 3.55 posi from a 67 GTO. Can anyone tell me steps to take to swap out the read end? a few years ago I installed boxed lower control arms and a rear sway bar so I've been at least that far into it. Any words of wisdom or warnings? Will I be able to use the same drive shaft?