I looked everywhere also and couldn't find a thing.... I'm guessing extension rings weren't so widely sold, hence scarcity on information...

I know the metering coupler on lens couples to the pin right below the name plate on body. Inside it, there is a variable resister strip. (yes, I took it apart!) So, I'm guessing, I have to couple lens to the tube to the body all metering stuff coupled together in order for metering to actually work.