I don't doubt your take on the existence of friction bands. But the pics I saw had what's called a 'pinion clutch', of which I've seen several in use over the years. I know from that book that's been recommended, I have it, and it's vague right where this discussion is centered. I also think I can see the clutch handles in the blowup of the parts ID, they are not labelled, a not-uncommon failure with books on technical articles written by non-techs, or non-users.
In MHO, that book is good for an overview, but far from being technical enough to build a donkey, save as a freelance job. I'd recommend it, however, just for the overview of the subject.
Also, I think someone just above referred to the pinion clutch as a 'jam brake'. If we're talking of the same part, that's technically incorrect. Also, from some practical experience with 'band-type' power transfer, there's the risk of slippage/catastrophic failure, esp. if the band lets go. The pinion-clutches are positive-lock systems OTOH.
And the other gentleman is right: there is no power outfeed, they used a second line w. block & tackle to drag the cable back to the site where the downed trees were. I think that's what the second drum was used for. That may be covered in the book; not sure where I picked up that piece of info.