Simon.
I am the first to admit it is not easy to sort out these pipes.
I have made a drawing trying to explain my assumption below. The drawing shows the port engine in order to make it easier to check with the u historia photo.
I guess it is bit easier when you add the larger flange of the transition piece towards the group exhaustvalve housing ( red dotted oval). The largest red circles indicate the pressurehull flange for the hull outlet on top of the group exhaustvalve.
From the exhaust manifold main cooling waterbend out you have a branch off (1) purple pipe going to the inlet at the bottom of the transition piece( 2). Out of the transition piece at the top (3.) From (3 )green pipe goes to the bottom of the endpiece( 4) and out at the top (5). The pipe now light blue goes down to the pipe between the main coolingwater valve and the main overboard valve.
Tore