I have e39 wheels on my m3 with the 74.1x72.5 plastic rings. They work excellent. My original AC Schnitzer wheels are provided with plasic rings as well. Either plastic or metal is fine. Also putting those rings in will center them properly on the hub and clear up a lot of vibration you likely have. +1 on using a wire wheel or scotch brite to clean the surfaces. I also added a little white lithium grease as well.
sent from my ATARI sc1224