Im mid build, and have just come to fit the 2nd driveshaft into the diff, and i have now noticed that one has normal thread, and the other has a left hand thread.. which shaft should be on which side, or doesnt it really matter? ive been trying to figure it out in my head, but i cant see it making a difference either way, as the driveshaft gets nipped upto the bearings which spin with the shaft. if it was nipping upto something fixed, then youd want the thread to be the direction to keep the nut twisted tight...

As you have said in your question the nut should tighten towards the front of the car so normal thread drivers side, LH Thread Passenger side!

HTH Mike

I think one side is slightly longer than the other too so they will only fit one way