How important is it to align the engine with the rest of the drive train?

How much variation from level and in line from side to side is allowable?

Ideally, the transmission output shaft and the differential input shaft would be exactly parallel. I get them as close as I possibly can. If they are off by too much you'll get a vibration. The engine in my wife Baracuda is out about 1/4" left to right without apparent effect.

Thanks for the reply