sOpattachhead is not working, in wow models the overhead and head is the same attachment point so you can use hardpoint 9 (sOPAttachHardPoint09)and hardpoint 13, (sOPAttachHardpoint13)depend on helmet types, for example for helmets you should use hardpoint 9. note: the default hardpoints actors in the editor are only filled from 1 to 4, if you would like to use more hardpoints you must creat a Site Operation (Attachment) or duplicate one from already exist ones. Important when attaching you have give the same id that you give in this creation.
rename it to sOPAttachHardPOint09
attachment querry methods: filter type: direct, select hardpoint in roll menu, index:9
now you have sOPAttacHardPoint9, so you can set it in the helmet actor fields.
note: Some times you can change the helmet models to the correct race, for example you creat a human unit with human wow model, and duplicate it to creat the troll version, the human helmet could attach relativly wrong from head, so you can import the troll version of the helmet. The better is that you import all the helmet types if you would like to use all race versions, some time it is not required but if you do all of them you cannot mistake.