I heard this also but it is not true because i have a j30 in mine right now and my drive shaft is stock . All i had to do is swap the rear covers and put some washers on the front bolts so it would hold the diff cuz the s13 bolts are smaller than the j30 holes.slow s13 wrote:and possibly get an auto drive shaft its like 1/2 inch shorter iirc, because the j30 diff is longer because of the abs ring on the input shaft.