The first thing is to decide on what angle you need. Then put the housing at the ride height . leave the perches unwelded u-bolt the rear in place loose but snug. Center the rear in the car . Now you can turn the housing . Have the out put shaft of the trans parallel with the pinion in the rear. After you find parallel . The turn the nose down the angle you decided on. I would stay at 3-5 for a race car with stiff front segments or calvert bars. Under hard acceleration the trans output and the pinion should run parallel.. If they are not parallel a constant velocity joint must be used
