Drill a hole or 2 in the flat face of the ring gear, noting which way the lead on the teeth faces and finally split with a chisel down between the teeth. Then if you don`t have access to a welding torch, take it to your local bodyshop with a welding set and they should heat it up and drop it on for you, again making sure the lead on the teeth are facing the correct way.
Hope that helps, that`s the way we`ve always done it.
John