Seem to recall an interesting perspective in some book or another. Riddles was going, Harrison had installed himself at Derby and was making his presence felt in the design office and so people were minding their P's and Q's. As was usual practice with BR Standards certain components were specialisms of certain drawing offices so following protocol a request was sent to Swindon, (not Doncaster, not the Valve gear company), for a double chimney - because this was where Sam Ell was .. who was BRs Draughting expert.. It seems likely that Ell wasn't consulted and Swindon just found a chimney about the right size - hence 2 x Dean Goods, expecting that, as with all things Swindon it would be right, and if not Rugby would tweak it. When it got to Rugby and odd things were happening... well the chimney had come from Swindon so it must be right/ must be something else that's wrong. Seems to me that in a period of uncertainty the 71000 project fell out of ownership and things got missed, I don't subscribe to the conspiracy theories. By some educated guess work or inherited tweaking the draughting for some of the Standards was pretty good ( Brits, 9F, 4 2-6-0, and 2-6-4, 3,2) On others it was nearly right and benefited from tweaks official (5mt) or on shed (Clan). On the 4MT 4-6-0 and 71000 it wasn't right. Not sure what 72010 will prove other than the boiler is perfectly good and with the correct breathing apparatus it will be a good Class 6 rather than a poor one but Carlisle 'Jimmied' them and already knew this in the 1960's .