Well....since no one has answered this question I asked about a month ago. I will. After watching several you tube videos and going to the Spicer website, I found out about "operating angles". It takes a digital protractor and measuring 3 angle points. Rear of tranny-( flat end of tail shaft or u-joint with adaptor ), center of driveshaft and rear yoke /pinion angle. Plug all 3 angle specs into the Tremec or Spicer calculator,(it does the math for you) and you'll find out your operating angles, which must be less than 3 degrees to be considered in tolerance. More than likely, no one on this site will ever need to know this, but , if you replace your stock tranny...you just might. My 5 speed project...moves forward