does a twin row run 1 cam ring or two?
While I am in no way any expert, and the carpenter mentioned in the second video that there are many variations, I would imagine that in a twin/triple/quad row engine, there would be a cam ring set to each row, as essentially the engine is being extended by just adding another complete set of cylinders (and operating mechanisms) on to the front of the existing ones.
Looking at this image:
https://en.wikipedia.org/wiki/Pratt_...p_R-2000_2.jpg it shows the front row's pushrods are actuated from the front of the engine and the rear row's (judging by the orientation of its rocker covers) are actuated from behind it, so needing two cam rings.
Edit: here's a better picture of a four row cutaway. You can see each row has a cam ring
https://en.wikipedia.org/wiki/Pratt_...ry_cutaway.jpg, although between row ones are shared, which means that effectively each row has a cam ring on each side, driving either inlet or exhaust valves.