I am looking for a posi-track differential for a 1964 to 67 GM A body car, Chevelle / Beaumont the like . This is the short unit I believe 54 /12" flange to flange? I would prefer a 12 bolt, unit with high gears ie 3.08:1 or 3.33's for street application. However, I would consider a 10 bolt with same ge...