The difference between a V23/MM case and V72 isn't so much in the rehaut, it's in the crown/stem height (i.e. the position in which the hole for the tube is drilled in the case).
Here is a comparison of my V72 6265 franken and my wife's MM movement 6263.
Valjoux 72; case is a Phong/JW case. Note the crown's position/height in relation to the pushers:
Valjoux 23; case is an early DW. Note that the crown on this is much higher/closer toward the bezel:
Rehaut on both. Gen silver dial is the V72; PN exotic dial is the DW:
BTW, for the record my old original DW from a few years back had a Swiss V23 that I had transplanted with no problems. A V23 going into a MM is a 1 to 1 swap.
For the few folks that had retrofit a V72 into their MM cases at the time, modification to the rehaut was necessary to allow the V72 to sit deeper in the case thus allowing the stem to line up center in the tube. The height difference is maybe less than a mm which doesn't sound like much, but when you're dealing with tolerances as small as those involved with lining a stem center in a tube, it's significant as the result could be snapped stems.