Simon.
I have no means to measure the angles, but am wondering about your blue casingdeck image. I the way of the lower wintergarden I guess the casing deck has a small 2nd. widening between frame 41+ and 47. See picture below. I have some photos showing KNM the decking in the vicinity of the snortmast see below, on the Kaura decking we did away with the wintergarden and the 2nd deckwidening.