Always thought it's a shame how the 21cm is displayed - the German artillery at Duxford is in a similar way, put in one corner as a 'captured artillery park'. Maybe that will change now there are more WW1 exhibits there as IWM London doesn't like to have exhibits anymore
I visited IWM in London and Duxford last month, I also visited Firepower, Royal Artillery Museum. It will take a long time to organize and post-process the pictures, but I will eventually post pictures from there too.