Alan the 2004r will accept the 604 /4L80E rings but needs to be stretched and shrunk to fit. Less than optimum after the trans gets heat cycled a few times. There are exact fit solid Teflon solid and scarf cut rings from a @#$%^& unit that do fit the 2004R center support. I was making them from Delrin years ago, like the 350 steady rest ring, but it was too difficult so went to the @#$%^&.
Are you referring to Toyota rings? I've heard mention of them but never asked what the application was and if they'd fit a stock drum. I'm glad I started this thread