I'm about 99% sure that the following answers are correct.
Is it really bigger at the nut? No
have bigger ss frets? No, but it does have those cool inlays.
and use entirely different pups? Yes, it has the single coils from the Cutlass and the humbucker is only on this 25th. It's a different humbucker than the Cutlass or the regular/bfr LIIIs.
The dimensions of the Luke III body and neck remain the same. However, the pickups and electronics are custom made in the Ernie Ball Music Man factory for that guitar.