I believe Bob also mentioned there are different grades of Delrin too. Maybe he will chime in if he sees this thread.
These are the SDP gears I modified to fit the Niagara. Before I installed them Mike announced he was going to make the brass gears. Given what a chore it is to install the geras I opted to just wait for Lionel's. You might be able to see how close the SDP straight cut gears are to Lionel's helical gears at the top.
Pete