I think they used sort of step-in method for bracing. The nocks on originals are simple cut in gooves, without any reinforcements like sinew patch under nock to avoid splitting as we see on modern replicas. The nocks are on opposite sides naturally.
The big bow is from only 4 cm diameter stock, the marrow chanell runs actually whole lenght in and only comes out on one end in the nock area.
The lower part of the tree is upper part of the bow, if this helps.
I dont think yew it is made of has 100 rings/inch, but it can be around 60 which is decent for european yew, which is stiffer than pacific.
The rings on big bow are not visible and the line marking the sapwood is relativelly faint.
But! I dont think they actually chased rings down on staves. They found a yew sapling on prefered soil type, which they knew will have sapwood thin (means also high ringcount), cut it down and made into bow. The back is perfectly smooth, the belly is scraped and has toolmarks.
I think that the big bow with its 191 cm of lenght and some 180 cm of effective could work well for draw of 30创. (Or better could be tilered there). They have width taper similar to later english warbows, which makes them circular in shape.
So as I made me recently 69创 longbow, which is 90#/30创 from second rate yew with lots of sapwood on it, I think its doable 100# + range.
http://sweb.cz/hawkwind/myyewbow.JPGJaro