240sx-venezuela

Hi there, Long story short, Im currentlly doing a manual 6 speed swap, I have everything installed, but I'm having problems with the passenger side axle, I bought it new and the part number is correct, is a Surtrak NI-8188, Ive read on other side that some people swap the outer part of the axle for an automatic since the lenght is too short, and Im wondering why this? What is the difference betwen an auto and manual apart from the axle lenght diffefence, why even the manual transmission axle does not fit correctly even the axle bracket sit 3/4 inches apart and does not bolt on, maybe the axle bracket for a manual is different from the auto, but dont really know, if anybody could help, I will apretiate it