I believe that all MM guitars (with the exception of silo bass) have the same scale length (25 1/2"). So, the length of the fretboard is the same on all models (ok, the 24 fret ones are a little longer for those extra 2 frets, but it's the same scale length).
I remember Luke having a really narrow nut width. I liked that.
EDIT:
Turns out all MM's except the JP6 and 7 have the same nut width, 1 5/8". The Morse is also slightly wider at the last fret, comparing to the Axis', Silos, Luke's, etc.
Ah, so you're talking about nut width... Sorry, it seems I misunderstood the question.
BTW, you can find a lot of information and measurements at http://www.ernieball.com/mmonline/