Then the 90's duo isn't really going to work for him very well.
The new Jagmaster neck is perfect on a 90's duo. As both bodies were intended for compensated necks. Mine needed to be shaved a hair, but aside from that it's like it was meant to be.
The otherway around though... you end up with this goofy little air-light 22.5" neck on that big ass heavy Jagmaster body. and while it's a compensated neck and should intonate just fine it's going to be way misweighted and frankly ugly.
As for the new Duo's I'm not sure f they are a straight 24" or a compensated 24" so aside from the heal not fitting they may not have been a workable match anyway.