G8 vs OOT G3 hairs
in The Commons
The G3 vintage OOT hairs I have -Topmodel, Georgia and Sporty Ponytail - don't come through the G8 autofit well. A bit frustrating, but the work-around is to skip autofit, manually tweak the position and then parent. Of course the new G8 OOT hair fits perfectly.

Comments
Hmm, I guess I got lucky -- I tried OOT's G3 Georgia and Cathy hairs and they worked fine. Used the "Hair-->Shoulder Length" autofit option.
This is on a character with the Elizabeth head shape (comes with V8 Pro) plus some dial twiddling. I only used one of OOT's quick style buttons, didn't try adjusting any hair morphs directly.
I've had autofit problems with some G3 clothing, but fortunately not hair (yet).
If the hairs use bones (for things like tail posing) then those will be lost in AutoFitting. One solution is not to fit the hair at all but to adjust it to more-or-less fit and parent it to the head, using a Smoothing Modifier to deal with the less bits
I used Sickleyields tutorial for fitting clothes with bones to the G8 character on SWAM's H.Lee hair and OOT's Sporty Ponytail hair and it worked and did not lose the bones. The tutorial is voer at Deviant Art. Here is the link
http://sickleyield.deviantart.com/journal/Tutorial-Convert-Clothing-G3-to-G8-G8-to-G3-686682065