The only major difference between original and 2nd version was pilot and weapons (eldar weapons got a redesign - going to the triangular barrel cluster of the scatter laser). The legs are identical to the originals. The original pilot was suspended in an exo-harness (his legs moving caused the walker legs to move, I'd assume). 2nd ed version went to the seated pilot.
These two are on the same height bases (flat 60mm).
Hips appear to be at the same height. Pilot appears to sit higher, but it's also at a shallower angle and tilted back more.