As far as I recall, the aperture was regulated by two blades forming a squarish opening. The blades were operated by the light meter that sat straight above the bult-in lens. In front of the lens there was a mechanism that locked the auxiliary supplementary elements in place.
The image circle for 2x8 optics is very much smaller than MFT and the back focus would also be very short, so even if you liberated an original leica front (and hence destroyed a potential collectors item) it would not work. (Buy the set of supplementary lenses if they are cheap and wait for the market to really arrive. Some of them are uncommon, but there are fewer collectors of the totality of Leica photographic products than of their 35mm stuff) .
p.