Yes they did. I remember reading about it being on Dubach and Doug Henry's bikes. If I remember correctly it was to create more back pressure at certain RPMs?
I have seen those photos with the twin pipe head and the megaphone.
This pipe doesn't appear to to be utilizing the EXUP device, or the crank breather that is routed back into the head pipe like on Jimmy Buttons bike that was featured in DB a few years back.
Any images that show either would be appreciated.
I have some pictures in a old MXA magazine which show a canister that is fed exhaust pressure into the top of it from a tube braized into the header pipe and has the crankcase vent tube going into the side of it also has a small hose coming into bottom of the chamber aswell . The desciption with it says that it has a diaphram inside that seperates the two and the pulsing of the two stops the oil foaming up. If this is what your looking for I could scan the pics (reasonably good close up) and post if some one could tell me how?