I had the same problem. The vent holes were in different places on certain years. I just threaded a bolt on to the old hole cut it flush and welded it up and then made a new hole where I needed it. Sorry for the run on sentence.
My car has the original rear end in it. But what I don't understand is that the rear end line set was bought as a set? So if the passenger side line was two inches too short, it would seem that the drivers side should have been two inches too long??? But it appeared to fit fine??