Similar but not the same... The barrel is almost the same size at 14ft 10ins long with an extra 3 inches on the max diameter for the 47 (6ft vs 5ft 9). The tube layout is different as well. According to the RCTS the firebox was the same at 10ft. The end result is a grate of effectively the same size at 30 and a bit square ft with the total heating area at 2556 square feet on the 47 and 2312 for the castle. The no7 boiler was always held in high regard by the crews and at least one Old Oak fireman that I spoke to maintained that the 47 would do anything a castle could and burn less coal in the process. He was in a position to know but I guess time will tell. The newsletter announcing the change in cylinder plans implies that the new boiler will be mounted 2 inches lower so as to comply with the current NR limits. This allows for correct size boiler mountings. The new cylinder blocks have therefore been designed to suit.