Mdlvis. Open the model in Mdlvis, Go to Modules>Sequence editor>Bones>select the invisible parts/their vertices(in this case shoulder pad, head and weapons)>select their bones(in this case the model you posted was edited Eredar warlock model, so what I did was extract the original Eredar warlock model from the MPQ, open it in Mdlvis and you do the same process when you open it; go to the bones tab, now you need to see on which bone are certain vertices attached to; for the head, select the head vertices from the original EW model and in the right corner you will see the name of the bone that the vertices are attached to, repeat the same proces for the shoulder pad and for the weapons, select the original parts of the model and see on which bones are the vertices attached to. Now when you know the names of the bones you need to attach your geoset parts, it's easy, select those parts and attach them to the bones that match with the original.
