Does a fighter/illusionist, for example, use the better of the two classes' attack matrices and saving throws? If not, how does this work? Thanks in advance.
You can simulate 1st ed multi-classing in 3e by using the gestalt rules and applying a level adjustment.
+2 LA seems about right to me, and I think that was the very rough consensus last time I saw this issue brought up. (It means a cleric/wizard's spell-casting would track with a mystic-theurge, for instance. )