Use Magod editor.
Open any ladder model that has those attachements. If your model is based on other bliz's model better open that one.
Go to Windows -> Node Manager and look for 'Chest Ref', 'Weapon Ref'.
Now open your model in Magoc and again, go to node manager but this time right click outside any node and select 'Create Attachement'. Press PPM on new created file and click 'Edit Node'. The only thing you will have to edit are 'Pivot Point' fields: X, Y, Z. Just CnP values from previous opened model here. Remember though that if you are going for eg 'Weapon Ref' look for nodes that refer to hand in which weapon in hold so you won't screw animation in game.
EDIT: I though you want add attachements to model which has no one.