THis is something another person wanted to know on the mamiya site, it seems he found an address where someone did adapt the RZ WLF to an RB. Check this site out...

http://www.photoethnography.com/Clas...html~mainFrame

MAMIYA SITE QUOTE.............
Hello there: I am sure such combinations are not encouraged but I happened to purchase a RZ WLF at a really cheap price and I own a RB-Pro S body. Turns out they are not compatible but the reason I bought is with the hope that they can matched eventually. There is at least one reference on the Internet of such a match

http://www.photoethnography.com/Clas...html~mainFrame