Latest images coming from HBSS of the boiler progress show the completed delivery tray for the feed water. This is located with the left hand end in the first picture under the top feed with the tray pointing forwards and down.
A brief explanation is provided here:
The location of the water feed into the boiler has a significant effect on the life of the boiler. Boilers tended to pit in the area of the water feed, and dissolved solids would be precipitated as scale on the barrel, affecting the heat transfer.
In the mid Victorian period many locations for the boiler feed were tried, but clack boxes (valves) on the side of the barrel were a common option. Towards the end of the Dean era a location one each side of the back plate of the boiler became preferred. The arrangement is obvious on photographs of Steam Museum's Dean Goods. This arrangement persisted on some classes as late as the 1930s.
After a brief and unsuccessful flirtation with feed on the underside of the boiler Churchward decided on his own arrangement of top feed, inspired by American practice. In the GWR implementation top feed meant that boiler water was introduced through the top of the boiler into the steam space, and delivered onto trays. These trays sloped down to the front of the boiler barrel where they had notched ends so that the water fell onto the main water in the barrel in a series of fine streams. The trays tended to catch the scale and it could be washed out from there.
In looking for a suitable drawing to illustrate the arrangement, this drawing of The Great Bear turned up from the GWS archives, which interestingly shows a time when Churchward was still experimenting as it appears to show the top feed tray but with it sloping backwards towards the firebox.