Owing to height restriction rules the locomotive had to be reduced in height to comply with the Network Rail loading gauge (the maximum permitted height for steam engines being 13ft 1in and the original height of the kings being 4 inches over at 13ft 5in). This required the fitment of a cutdown cab and shorter safety valve cover alongside a shorter chimney. The shorter chimney however adversely affected the draughting. A new design of blastpipe with four nozzles was designed and fitted to the engine which after early indications had eliminated the draughting issues on the engine. The other preserved "King" class locomotives 6000 "King George V" and 6024 "King Edward I" are both fitted with double chimneys and therefore it was not possible simply to use the same proven blastpipe and chimney arrangement on 6023.