I've noted an oversight in the instructions for drilling holes in the boiler backhead in part 11. The illustration on page 42 shows the position of only six holes to be drilled 1.2mm for the wash-out plugs (A). Checking images of Mallard's backhead on the web shows an additional wash-out plug between the water gauges and under the regulator gearbox. This is confirmed by the illustration of the backhead on page 216 which shows this extra wash-out plug. I'm attaching the relevant illustrations from the magazine which I hope clarifies all this. In the first, I've added the additional location of the 1.2mm hole (A) in blue ink.
Unlike the Flying Scotsman build, Hachette has not recommended painting the backhead before attaching the various fixtures and pipework, so it will be interesting to see how this is covered in a future part. I have started to build my backhead by drilling all the relevant holes followed by painting the backhead and I will then start attaching the various fittings. I am currently sourcing copper wire for the pipework on the assumption that Hachette will be advising painting the brass wire provided with copper paint. This was the approach taken with the Flying Scotsman.