Well to be honest from what i ve heard and experienced with parts Davidsen's cases have their own construction..
They are bigger with bigger glass, different cg and screws, bigger dial hence the only thing interchangable without mods with the 'genuine, jimmys and regular reps' is only the caseback.
I never had a Davidsens watch to be honest for the above reason + the awful font on the dial... (the Amerigo Vespucci though has a very very nice font..)
I think that he does what all the rep manufacturers do.. having 1st 2nd and 3rd versions for people to upgrate