Dave,
Two of those sources drink the same KoolAid that you do, and none of them is specific enough to design a blender with, let alone an aircraft.
I recall the 50 HP number for the S76B precisely, since we designed the Fantail and its ducting to match the conventional TR power at half the disk diameter. I wrote a paper for the AHS forum in 1992(?) that published the HP vs thrust for the TR and Fantail, it is surely available in your tech library. If I felt like busting open the boxes in my garage, I'd post a copy! BTW, the S76B eats about 1060 HP in a hover, 50 TR HP is therefore about 4.9%. That is slightly hig because the 76 TR is designed for 50 knots side flight, thus it swings way too much paddle for low thrust efficiency. Most TR's are designed for 17 knots of max sideward speed, thus thrusts 1/2 of that the 76 can produce.
Even with the Koolaid cocktail, Makhayev gives his coaxial 10% more drag in cruise, with the concurrent reduction in range. If your 60 second analysis held water, designers would kill for the numbers you think you'd get. Nobody is running for the patent office, Dave!