You actually don't need to convert it. And, that convertor mentioned isn't ideal, at least I don't like it. Here is how to do this without autofit and without conversion.
- Load G8 character then unselect G8 character
- Load G3 Hair asset without parenting to the G8 model. You do not want it to autofit the hair asset.
- Select the G3 Hair asset then click the hamburger (3 horizontal lines) menu in the Scene tab then
- Click Edit and select Scene Identification
- Change Compatibility Base, Auto-Fit Base, and Preferred Base to /Genesis 8/Female then hit accept
- Right click on the hair asset and select Fit "Hair Name" To ... and fit it to your G8 character.
- Done
All the G3 morphs for the hair are now usable with your G8 model, without all the extra garbage that the convertors add during converion. This works with almost every hair asset even some of the more difficult to convert Goldtassel hair assets.
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Here is Addy Hazel for Genesis 8 with OOT Topmodel Updo for Genesis 3.
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Here is the partial list of morphs. They are the Genesis 3 morphs without conversion or modification. There are no added morphs either.
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Same hair using ponytail option and using the sliders to curve it to the left and forward to fit the pose better.