I tried following the instructions here but - http://manual.reallusion.com/Character_Creator_3/ENU/3/Default.htm#Character_Creator_3/3/07_Head/RLHead/Morph_to_Slider.htm?Highlight=RLHead
My sliders morph the entire body. Not just the head.

They tend to that. In sure you start with the base character . No morphs . If Genesis for instance.. Load genesis  base in scene.. Chose current as starting morph... If morphing just head insure target morph . Genesis has no morphs but the head. They may be some slight change in body.. But very little . As long as the starting character and target don't change body shape

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Alienware Aurora R16, Win 11, i9-149000KF, 3.20GHz CPU, 64GB RAM, RTX 4090 (24GB), Samsung 870 Pro 8TB, Gen3 MVNe M-2 SSD, 4TBx2, 39" Alienware Widescreen Monitor
Mike "ex-genius" Kelley

Thanks for the tips. Ioaded the CC1 female base and save it as an iAvatar. I loaded the RL100 head on the CC1 base than resaved the morph slider using the CC1 iAvatar as the source. Then I loaded a CC3 base and used the fixed morph slider.