Steam lance valves seem to have been at 4 o'clock up until 1926. There are photos in Russell (p152) showing them on 5006, 4076 & 4081, and in Cox "Chronicles of Steam" on 5000 at Carlisle. See also photos at Railonline https://www.rail-online.co.uk/p721368492/hD5626BDA#hd5625449. The things that look like smokebox door clips are visible on various photos of the exchange, but I haven't seen them anywhere else. One might speculate there was an issue in the very early days that was later sorted with an improved design.