If you get to act 3 hell in classic, you can convert to expansion, and you end up in act 3 hell in LoD. There you can do travi meph ( if the crusher is too weak to get it done in classic ) and do diaruns in hell for massive xp.
However, if you are in act 2 hell classic and convert to LoD, you will end up in act 4 nightmare.
All of this can be done as a lvl 1 char