DHfan, once again you add to my (our?) education. As you say, taking four drives off of the camshafts gave an immediate speed reduction as well as a more stable one. The sheer compactness of the Sabre can be seen from FED's pic of it. I must admit that I tend to characterise such cutaways as a "suitable arrangement of cogs and levers " so missed the design features that you point out.
It all rather reminds me of a "pilots watch" that my wife bought for me in Switzerland (no, not the 'B one!). Other than gently pointing out that the last place to buy a Swiss watch should be Switzerland, I also rather ungenerously queried what made a watch a pilots watch, other than that it should keep accurate time? When the interior arrangement of cogs and levers refused to operate further I took it to a watch repairer. He managed to get it working again but made the observation that, "this watch is too clever for its own good". Perhaps the same might be said of the Sabre?