[philofab]

Driveshafts have to have the same angle on both ends to eliminate vibration. When you move the pinion left or right you are inducing the same angle on the front and rear u-joints at the same time. The factory does this all the time for gas tank, exhaust, and suspention clearance. Take a look under 70s ford vans, the center section on the rear end is offset on one side by about 8 inches. The engine and trans are not offset.

If for some reason you can't create the same angle on both U-joints you need a double cardan joint (aka CV joint) on one end to eliminate vibration. Caddilacs and Ford Broncos use these from the factory on driveshafts. Broncos use them because the driveshaft is so short the angle is extreme. Caddilacs use them because the pinion is downhill to create tunnel clearance.

I centered the housing on the rear end I just built for looks and to move the driveshaft over so I could fit a torque arm next to it in the stock tunnel. Things that aren't symetrical drive me nuts.