The wing of the 747-400 was a totally new design from the previous 747s. The easiest way to tell the difference is at the wing root, when you are standing right at the L1 door. Where the wing meets the fuselage is more blended on the -400, of course if you look down on the a/c you can see that they wing is dimensionally similar but overall of different design. Strangely enough a good way to examine the difference is to look at a model of the 747-200 and the 747-400. I have a 1-144 scale United 747-400 (Revel) and a 1-200 scale KLM 747-300 on which the difference in the wing is obvious, aside from the winglets.