the mr fantastic arms are located in 'actors' as '20_mrfantastic_arm_left (right)'. i believe that is for the animations. for recoloring the arms to match specific skins it think its the files 2050, 2051, 2060, 2061, 2070, 2071, and 2080, 2081. you may have to recolor the effects too.
hope that helps. if you're asking how to deal with rigging them, i have no idea.