I'm not sure I understand why you would build it to fit v4 and then shape it from there to fit your target figure.  Why not build it to fit your target figure from the start? Am I missing something?

 

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Always make new content for V4/M4 first, even if you don't plan to release a V4/M4 version. V4 is the lowest common denominator and all conversion utilities works with it.

To rig in Daz Studio

In Daz do not use auto-fit and do not make a version for Genesis-Base made to stretch to fit other figures.(The recommended procedure from Daz). It will look like plastic. Instead, resize your V4 model in a modeling program to fit your target figure.

Then to rig this new obj, use the Transfer Utility with two special settings,

Item Shape: Current

Reverse Source Shape From Target: Check

That is all there is to it. I promise you that you can hunt for months without finding this information. And, this will work for Dawn from day one you can be sure of it.