Paul,

 I came across these photos from old RX-7 discussion groups.  It appears
Mercedes did the original research on the design.

The links are here for anyone interested.

http://www.rx7club.com/showthread.php?t=735888&page=3
http://www.rx7club.com/showthread.php?t=735888&page=4

It is unclear if the impellars are still available however.  Perhaps
someone at Seven Stocks rotary gathering might know.



Cheers

Doug in Japan