____Driveshaft Question??

You need to cut it down 1.6 inches the difference is the 81/4 pinion shaft is longer which means the driveshaft has to be shortened. The u-joints are also different, you will need one for an 81/4. I have a driveline that came out of a car with a 81/4 if you need measurements from the ujoints Was that measurement of 52 1/2 from center to center of the caps? Ask your driveline shop how they want you to measure just to be sure. I'm getting ready to do the same swap, and glad you had that measurement, saves me from having to crawl under the car.
Bruce