So, my prediction is now scuppered!
'Duchess of Sutherland' is now unable to attend the gala & has been replaced by LNER B1 No.61306 'Mayflower'.
https://www.bluebell-railway.com/wha...ants-of-steam/
I had seen that 6233 had been failed with valve prior to last Saturday's Norwich-Chester railtour, which was diesel-hauled instead, but the information on the Bluebell's website or facebook page doesn't make clear if this is the reason for the non-attendance.
https://www.railadvent.co.uk/2019/09...fore-tour.html
Tony