Another way.

Line the 2 figures up the way you want. Save the PZ3 for future use.

Export the 2 necks as objects. Import the 2 necks into modeling app and cut them, add what verts are needed to match each other and slice them together. Re-shape the splice to look nice. Export as new .obj

Import that neck back into your saved PZ3.

Export the V4 head, with possette body and the new neck. You can hack the possette Cr2 to point to the new figure .obj and with some JP adjustment you have your new working figure. MorphManager to transfer the V4 head morphs to the new figure. Should work.